Hotels are probably the biggest thing I would want in-game right now! Basically For Rent, but make it a hotel!
I’d love to be able to place them in vacation worlds like Selvadorada and Granite Falls also, but I’d love to specific activities like other people have mentioned, room service, Aquariums (as mentioned!), ownable lots, but also the ability to categorise what kind of hotel your sim is offering or staying at. Is it a bnb, resort, hostel, etc… I’d like to choose!
And, of course, tasks and chance cards which affect your star rating!