Big agree on the dance thing, I've been wanting a proper dance skill expansion/overhaul for ages. The fact that all the sims basically dance the same to nearly every type of music alone is so, so frustrating.
Personally, I feel like there's already an overwhelming amount of radio stations, but maybe that's cause I have a lot of packs. I'd rather there be some option to dance to live music somehow, and, like you mentioned, some concert and opera as well, maybe some singing careers and expansions with an addition of more styles beyond just the karaoke type thing that exists with City living.
But yes, at the very least, I'd like them to add more skill levels to the dance skill, which could include some things like ballet and musical theater type dancing maybe. And for different dance styles to match the music that's played. And partner dancing. Those 3 elements would probably be my top priority, with hopefully updates to get famous that at least changes the "musical theater" dancing to more appropriate animation (right now it's literally jsut the same as the dance work out from the fitness pack and looks ridiculous.)