Agreeing with everyone saying more relationships in CAS. Adding grandparents without having to create a parent, unmarried couples, cousins, etc..
Also I have a mod that kind of does it, but sims to only appear in the world they live in or nearby worlds. I consider most worlds in groups that are nearby, like Willow Creek/Newcrest/San Myshuno, Del Sol Valley/Strangerville/Oasis Springs, etc. and I don't mind sims visiting nearby worlds. As that's my personal opinion on what counts as nearby, I wouldn't mind even if they just stuck to their own world. I'd also like to mark unplayed households as living in a world for it too. I have a mod that mostly keeps sims in their own world, works well for most things but a few things override it (eg. sims sessions, student hangout lot trait, will bring in other sims) but I'd love it officially in game. It really bugs me and I know they can do it as there is a mod.
