Regarding the actual Sims, I wouldn't mind a combination of TS2 and TS3. Favorites, likes/dislikes, star signs, turns on/offs (attraction system in general) and more traits than we get now in TS4.
I also kinda wish they'd go back to world building like we had in TS2/3 where it felt like we were entering some sort of show or movie in progress (Where's Bella? The Capp-Monty feud, etc...)
I don't really care about babies, but just free the babies so I don't have to hear about it anymore.
I like the current age system we have now. Baby, Toddler, Child, Teen, YA, Adult, Elder. Anything else would just be a waste to me.
I want the old system of occults being added/expanded in every pack. I want weirdness and occults in every pack. Yeah it's a life simulator but why does it have to completely mimic real life? I can go live real life and not play the game. And I do NOT want occults to only be temporary like plantsims are now.
A combination of TS2/3 memory system where we get automatic memories with breakups/births/marriage etc... but also custom ones if we wanted.