) No socials and modern social things. SimSity is a greate game about building city, not communications.
) No modern paid ingame things. SimCity is a great game for brains.
) No "modern" 3D. It's suxx near good 2D pixel art. It can be 3D model, but it have to be rendered to 2D. SimCity is a greate game with excelent isometric graphics. Do not lower the bar.
) Good API/editor and manual for custom extensions. Central Store for it. SimSity is a game with a great authority.
) Better transport integration to itself. Time of transport structures building (not instantly). SimSity is a game with a greate RushHour addon.
Optionally
) Some new game parameters like culture (like education), gasification (like water)
) More complicated and transparent RCI. May be immigrants and the immigrant problem from Europe?
) Bugfixes (like useless IAg)