Expansion pack requests:
The ability to barricade units in buildings (for land maps).
The ability to put units in vehicles so they can shoot out of them.
The ability for units to jump on animals like tauntaun's and ride around on them for speed:
The ability to play as different species or factions -- i.e. play as pirates, etc.
Ranking for units -- i.e. like in Generals -- so you work on having the units survive because they will get better. I suggest having them gain a strip/rank if they survive an entire land or space battle, not during the battle itself. Then give them a little easy to see marker to show their stripes.
Dimplomacy -- trade with pirates or hire them as mercs, declare temporary truces, trade land for space and vice versa, etc.
Jedi and Sith classes, where you can actually create padawans (you can build an academy structures) and as they gain rank via combat they can build up more force powers and/or saber skills up to the level of Jedi or Sith. Imagine massive RTS saber/force battles with Jedis and Siths fighting it out.
Some kind of sea units with water and underwater abilities (stealth with other units having anti-stealth counters -- sort of Star Wars submarines) -- naval type battles are always fun.