I would definitely like a Skill that would allow making of soft furnishings, curtains and so forth, but also sofas and beds and things, basically the furniture you can't make with sculpting (at least I don't think you can make those with sculpting). I dream of having a house entirely built by the Sims that live there.
I'm sure they'll add pets of some kind at some point, but when they do I'd like them to add the ability to make monstrous insects via transmutation, ie combine eight beetles into one huge beetle that you can take for walks and stuff.
I'd also really like them to add the ability to have your kid have a paper round, also I'd like them to add baby sitter, repairman, pizza deliverer, maid etc as playable careers / professions. Couple of reasons, one it just feels strange that there's these jobs that exist that your Sim can't try and do (I mean is there some kind of really strict union that only allows Sims with no home or relatives to join?) and secondly it irks me that if you marry the maid he or she automatically gives up their job (by the way has anyone married an npc fireman since ambitions, did they remain a fireman?).
I'd also like favorites to be listed on the friends / acquaintances tab, currently if you do the 'get to know' interaction one of the things you may find out is their favorite colour, but only if you, the player, are watching for the bubble above their head as they talk, and then you would have to physically make a note of it somewhere because the game doesn't record it (on a not entirely unrelated note, why does a pop-up appear telling you the sex of the future baby if you're playing the doctor but not if you're playing the mother who has asked the doctor? Sure you can watch for the little blue or pink thought bubble, but that's not always convenient).
That's all I can think of right now.
