It's why I'd suggest a new medieval game to have each neighbourhood be it's own Kingdom. It gives so much room for expansions there to add all kinds of new options, and they could still play quite a bit with history there. Covering all of history would be too big for sure, but early to late medieval with some renaissance and steampunk stuff could work. It has so much room for expansions.
Here's some rough idea of what they could do with Sims: Fantasy realms or something similar:
-Basegame: Includes a Northern european neighbourhood somewhat similar to Sims Medieval along with the architecture, furniture and clothing styles you'd expect. Also includes a Italian city state/Kingdom style neighbourhood with more Mediterranean architecture, furniture and clothing.
And a Wood Elf Kingdom for something more magical, a forest neighbourhood with magical spots and mostly home to Wood elves with associated architecture, furniture and clothing.
Magic would already be in the base game, but is divided in different spell schools and later expansions can add new spell schools. Base game has Druidic magic, Arcane magic (covers basic magic spells) and Fire magic. You can set a forbidden magic type to a neighbourhood, or can forbid all magic. Clearly wood elves would forbid fire magic in their Kingdom.
Basic ship travel would be in the game, similar to Sims Medieval with maybe a bit more trade in the Italian City State.
Aside from humans, Wood Elves would be playable and ghosts would be in the base game and could also be playable but can't be made in character creation.
As for skills, sword fighting, archery and jousting would be included. The base game has horses and even a Unicorn can be found but requires a lot of work to make it your horse. Would also be some other proffesion related skills, the basic stuff that would be needed.
Mage would not be a life state, but could instead be a trait that enables a Sim to learn magic. It could be possible to obtain that trait in some very elaborate way too which could be a pretty fun goal for a Sim to pursue.
Full expansions:
-Dwarven halls.
Adds an underground Kingdom of Dwarves and makes Dwarves a new playable life state. Also adds architecture, clothing, weapons, furniture and such in dwarven styles and adds new skills like beer brewing and expands the armour and weapon crafting skills to have a lot of new options. Also adds some new options to get food, new dishes and stuff and other things that come with living underground. No new magic.
There are big NPC ogres also living underground that can be dangerous, but can also be befriended if you play careful.
-Vampire Counts.
Adds a transylvania styled neighbourhood with a grand gothic castle, lots of gothic fashions, architecture, furniture and such and of course adds the Vampire as a new life state and adds Blood Magic as a new magic type.
-Arabian nights.
Adds a middle eastern style Sultanate neighbourhood with a sprawling desert landscape, an oasis and all that and adds the Genie as a new life state to be found. Of course the magic lamp is a new object here that lets you make wishes. Finding the lamp should be a real challenge and not something easily obtained, but the wishes would be something good. Like a Sim can wish to be a mage of course, but also to become any of the life states in the game and also added in later expansions as playable. Or a crazy amount of wealth, or to become the new ruler of the neighbourhood they live in. Water magic would also be new, and would work great in the dessert environment but also at a sea.
There could also be skills associated to Medicine and greater learning, as is fitting for a middle east inspired pack and of course the Merchant career could be revamped some, getting new options.
-Northern realms.
Adds a snowy Viking style Kingdom where it is always Winter unless you change it with magic. Ice Magic is added in this expansion of course, and lets a Sim create many things from that, like an entire house with furniture even but it requires a lot to have constant winter or it will melt unless they mastered Ice Magic completely. Adds trolls as a new life state, they are very ugly but human sized. Sims can be cursed into Trolls by some events. Sims are scared of Trolls unless they are brave or have other traits like that, or become friends with a Troll. Trolls are uncomfortable in sunlight and can turn to stone if left out too long, they won't die like Vampires though and a Stoned troll can be unstoned through alchemy or magic use. But if the statue is broken, they die.
Of course the pack adds all kinds of Viking architecture, a Longboat, clothing, lots of beards, etc.
-Fey realm.
A more magical version of the Wood elf realm pretty much, far more colourful and like the heart of magic, inhabited by the new Fairy life state.
They are smaller than regular Sims, bit smaller than Dwarves even, child sized like Halflings but clearly they'd look like tinier adults. Also adds Fey magic, which is unique to Fairies but Sims with a Fairy parent or grandparent could learn it.
Adds all kind of Fey style clothing, furniture, etc. It would give the build options and everything to build houses for these smaller Sims. Child sims could walk in there just fine but Full sized Sims would not be able to enter the smaller doors. Dwarves can, but their furniture and homes are human sized since they are broader.
-Realm of the dark lord.
A dark realm that offers more evil looking clothing, furniture, some torture devices (nothing graphic) and new ways to be evil, new traits related to evil and also adds the new storm magic to aid in that. It's pretty much more of a Mordor type environment. Orcs are a new lifestate added here, not inherently evil. There's nice Orcs who want to change things around, and of course you can let Orcs live elsewhere. People might be a bit scared of Orcs though, outside of this realm. But inside this realm, nobody looks weird at scary races and they can walk around openly.
-Eastern realms.
Adds two neighbourhoods instead of one: One a Chinese Kingdom, the other a Japanese Kingdom, but there are other Asian influences available as well. It adds new weapons, clothing, armour, furniture, architecture, etc. Also adds Light and Dark magic, A Ying and Yang idea, two counterparts. While it does not add new life states, it does come with pet Long dragons and a larger Long Dragon that can be interacted with in it's cave and might reward clever Sims who prove sufficiently wise to be worthy of their gifts.
It also adds expanded options for life states from other packs, like adding a Terracota soldier appearance for Golems, letting Vampires be hopping vampires and some new ghost options as well.
-The Gnome Enclave.
The final big expansion, the Gnome Enclave adds steampunk elements to the game. A new inventor career that can create all kinds of new things, Gnomes added as a new life state, as big as fairies for convenience, so their furniture and such are that same size but the expansion also adds stuff for regular sized people or maybe like in Sims 4, the resize option could be used on these objects but can only be one of two sizes.
Airships are also a thing here, and the new magic is golem crafting, allowing Sims to create their own Golem companion which would also be a new lifestate similar to robotic Sims we have seen before. Instead of chips, different runes can be carved on them to give different functionality. They can be made of various materials too: Stone, metal, crystals, etc.
And now game packs:
-The Swamp.
A swamp neighbourhood that adds less content, but does expand fishing and adds some swamp adventures. Also adds the new Goblin life state, and more raggedy buildings, shacks, clothing and scavenged looking stuff. Scavenging is something new here, which Goblins love to do.
-Halfling town.
Something similar to the Shire, but obviously without infringing on copyright. A nice peaceful place that does not add any new magic, but could add some new leisure activities and pipe smoking. You'd get all kinds of cosy furniture, delicious foods and comfortable clothes here and of course Halflings are added as a new life state.
-Crypt pack.
No new neighbourhood, but adds several Crypt and graveyard lots, sometimes with a chapel of sorts. Places of adventure and death.
It adds Necromancy magic as well as two new life states: Zombie and skeleton. Both are considered scary by most Sims. Zombies would have limited capabilities, Skeletons would be more free in behaviour but always see the Necromancer they are bound to as their master so do everything that Sim says. Unless it is the skeleton of a mage who maxed out his Necromancy skill, then it is a Lich then they have full free will.
-Pirate pack.
Adds pirate ships as new homes, that can lay docked in any neighbourhood with a harbour. Adds plenty of pirate outfits, a new active piracy career but also the ability to look for adventure at sea. It adds mermaids as a new life state, and also has some underwater dungeons to explore that only mermaids or life states that don't require air to explore without use of magic. With high enough water magic skill, any Sim can explore it.
-Witches and Warlocks.
Adds Witch hovels and a coven you can join as Warlock or Witch, expands Alchemy options and adds new Hex magic. Flying brooms and other witchy stuff are included of course. Witch/Warlock is a new profession and not a lifestate, however the expansion does add various temporary conditions and effects that Sims can suffer. Like turning them into a frog of course. Could also be a new Old hag voice set that really lets a sim cackle like a stereotypical Witch.
And now Accesoires packs:
-Dragon's hoard.
Adds a dragon cave destination, kind of like a vacation destination but just one lot. It's the ultimate test for your adventurer Sims and really added as a challenge. You need to gather a party of adventurers, a team can work together to use various items to slay the dragon and get access to it's hoard. Or try and sneak past to steal some of it, or try talking with the dragon to make a trade. If you give something worthy for it's hoard it could give something in return.
However if you kill the dragon, you can loot dragon scales and bones from it which can be used to make new armours ,trophies and weapons.
Pretty much everything this pack adds would need to be won as a reward, but it can offer a few dragon themed outfits and jewellery too.
-Royal clothing.
Adds a variety of crowns, circlets and lots of clothing in all categories fit for royalty. Pretty simple. Maybe a few new thrones as well.
-Enchantment pack.
Adds new enchantment magic which mainly lets you add cool effects to weapon and armour in a new magic forge, purely cosmetic effects. Also new wizard robes, hats and a few objects. The enchantment magic can do other things than those effects too, like genuine enchantments on objects similar to what in Sims 4 can be done with the handiness skill. Like make objects self cleaning.
-Grand library.
Adds a library lot with tall bookcases but also some hidden rooms that can be found. Many new book case objects, decorations, tables and comfortable chairs, nice fireplace, just everything a wizard might want.
-Barbarian pack.
Adds a new Barbaric trait for Sims to have, to act like, well, barbarians. Crude, direct, unconcerned by what people think of them, bit blunt maybe, not frightened of anything and don't shy away from a fight. Also comes with clothing, hairstyles, body paint, weapon and armour designs to really look the part as well.
-High Elf pack.
Adds High elves as a new lifestate, not a big change from wood elves but they work a little different. No inherent concern about forests and all that, more comfortable living in cities but do share their long life. They instead are more inherently ambitious, wanting to accomplish things. Maybe a bit snobbish.
-Jousting pack.
A pack that simply adds a lot of new horse barding, saddles, lances and fancy knight armours and helmets. Some shields and such for decoration too, and outfits fitting for servants to match the new bardings and tabbards too.
I could probably write up at least 20 more of all this, but I think the point has been made that there's room for a great many expansions, especially since no doubt people reading this would notice stuff they'd love to see in this that I didn't mention.
