I think most of the things you mentioned still are suited rather for expansion, than EU4. My picks would be:
- more buildings,
- better graphics,
- more small flavour adding features (like not binary religion and culture state for a province, some actions available to change those. Policies influencing your population more directly, not just throught events.)
- maybe some dynamic province borders
- Possibility to manage provinces more complexly and more easily (f.e. advisors for given regions, turning given province to more military or more economically developed regions),
- Possibility to create more complex army (not only inf/cav),
- more country-controlled investments. Roads, farms, etc.
- possibility to play in a more peacefull way, still archieving victory
- drastic random events - f.e. United States forming by taking land and being in a state of war, not only creating revolt
- more complex discovery settings (may be more similar to Civ)
- better chat in multiplayer!
- more multiplayer options to enlarge the community
- better net code to allow hosting for 30 nations without overloading NASA servers
- possibility to join-in-game for nations
- some custom victory conditions
I think ways to go are numerous. Game should be easy to play on a basic level, in the same time letting people controll their nation very complexly.