If too much is included in the base game the base game will be more expensive, and as people here point out, not everyone is into the same kind of game play.
With that said, I do agree that seasons is so basic that it should be a part of any basegame (costumizable or toggable on/off for those who do not want it). My reason for this opition is that weather has a huge impact on a world, and to have it as base would make a difference on how worlds are created. For one this would be an opportunity to really think about how a world will be used from the get go:
* swimmable waters in all worlds that it would make sense in
* the ability to skate on lakes and frozen boddies of water in the winter in worlds where winter is a thing
* sledding on slopes of the worlds in winter
* holiday decorations and things like easter egg hunts, winterfest markets in public places (not lots, but town squares and other open communal areas)
But also just the planning for weater when making a world. For example San Myshuno has an open air lounge and an open walled kareoke bar, yet is a world with heavy snow in winter. Plantet Honey Pop is so poorly built that it snows inside, meaning three original locations are useless in winter. In dorms in Britechester people freeze to death because there are no thermostats in their dorms (which can only be edited by cheat codes after you move someone in). This proves that weather has not been a factor when building these places. Add weather as a base game feature, but let those who wants to turn it on and off do so.
Another feature I would add as base game is the club system, the dance floor and dj booth, restaurant and retail lots (go to not own) because these are again features of every day life. I would also add some active careers and make all other careers semi active so you can play them if you want (and build their offices). I would also make uni-education base game, perhaps not active in base game, but so that some jobs were tied to some degrees.
The DLC I would have: pets (with more than just cats and dogs), fame, own your business (including the cafés, restaurants, night clubs, bars and retail shops in the base game), school (primary, high school and uni) and all occults, holiday (with resorts of different types).
