I'd like a hybrid of modern day Universe and htcp career. Where you have a major focus on one guy and make all his decisions through in depth stories like in htcp, but you can still play the rest of the shows and Universe style cutscenes and storylines unfold that you have less creative control over.
Rather than replace Universe, keep it AND bring back a mode similar to RTWM from the 2011 game. You can freely roam around backstage and interact with other superstars/divas. Improve it with more consequences and longer/branching/varying stories, though.
It can be done, but maybe not in time for the next game.