King of the Hill-themed maps would be nice to see, too. Instead of just "hold X kind of planets for Y minutes", there'd be an uncolonizable designated as "the Hill". You hold the Hill by keeping a capital ship in there. The more capitals, the faster you gain points/time inside required to win.
Basically, think Halo, but on a 4X scale.
A tech allowance meter like they had in the older C&Cs (RA2 and before) would be a cool addition. More epic, psychotic, frigate-fragging frenzies.
Who else wants to see people build nothing but colony ships, siege frigates, and scout ships the entire game?