I would love to see more romantic animations and interactions. Proper cuddling on both the bed and couch, online dating (I found it useful for finding "options" quickly), and maybe they can try to figure out hand-holding again? I remember they said somewhere that they tried it before, but it caused glitches whenever the two Sims holding hands had a Sim walk past them.
Maybe an attraction system? The Sims currently have no reason to be attracted to another excluding the fact that the Sim was Flirty and the other Sim was just right there. There's no crushes, no actual attraction, no compatibility, no reason for Sims to procreate at all excluding to just make sure they don't die out.
A reputation system would be nice too. Cheating is all too easy in this game. But if not that, at least the attraction system.
Couple dances would be nice as well, both fast and slow.
Somebody should mention this to Grant since apparently he's been pretty forthcoming lately. (I won't because I refuse to use Twitter)