I would love Faerie pack, but I'm afraid if we did get one it would be nothing but twee little fashionista pixies & tinkerbells and very little actual Fae content.
If I was designing the pack I would include the following.
CAS.
Ability to choose whether or not your Sims fae is a member of the Seelie or Unseelie courts (with different traits & aspirations for each)
Sims fae have a human and fae form, dependant on what court they are part of.
Clothing style 'cottagecore', folk and Medieval inspired styles for women. Same for male Sims but with the addition of Victorian & Edwardian inspired male clothing (waistcoats, riding boots, tweed, newsboy caps, etc)
Gameplay:
Ability to invite Brownies into your home to clean and repair things. You have to make sure to thank them & cook a special meal for them though or they will start breaking things. If you do something to insult them they will randomly set fire to things.
Ability to hire a fae as a hairdresser and stylist for a night out, but again if you don't treat them right or leave them a suitable offering, they will destroy your outfit, tangle your hair and/or curse you with a low hygiene bar for a number of hours.
Ability to form groups or gangs with fellow Sims fae. Unseelie fae form unseelie groups and vice versa. A meetup of both groups could be randomly called to attend certain homes or venues deemed to have insulted the fae, where mischief actions, or outright fights could take place.
If you play as a Sims fae then being near iron will make you sick. You can ask someone to remove the iron temporarily, but it will cost you simoleons & you won't be able to perform any mischief or mean actions for a certain period of time.
For human Sims, unlock certain items after meeting a certain number of fae - such as a potion or special herb to be able to safely travel to the faery realm, faery musical instruments, or a banshee's comb.
The same unlockable items randomly spawning in world, but taking any of them has a risk (eg taking a Banshee's comb could lead to a type of curse, playing a faery instrument spawned in world could make you and those around you sick).
The Seelie Faery realm accessible through a tree portal, but if you visit without first having unlocked, or found the right potion/herb to carry then you risk returning from the realm as an elder, or if already an elder your Sims life is shortened by a few days. The Unseelie realm is a hidden realm with its own risks and rewards (as per the example below).
A Banshee (Bean Sidhe) may randomly appear in different areas & keen a mournful song when there are elders with one day left to live. You can interact with her and ask her to send you to the Unseelie realm. Once there you have the option of approaching the Will 'o' the Wisp tree to ask for extended life. One of 4 things might happen (2 good and 2 bad) - you could be granted immortality, you could be given an extra life cycle, you could be driven temporarily mad, or you could die.
A couple of lakes in different parts of the world you can swim in that might grant you a +1 positive moodlet, but be careful because you might also be pulled in by Peg Powler & left soaking wet and given a +2 embarrassed moodlet.
Build Items
Iron bars/grating for windows as faery protection.
Iron wall hangings for outside.
Strings of bells that can be hung around hedges or used to decorate trees to distract faeries away from the house.
Alternatively build items that will increase the likelihood of a faerie visiting you.
A basket to leave by the door for offerings if a faerie does visit your house.
That's all I've thought of so far. :)