GC does not fit the MP mold.
Do it like dozens of other companies have done when they wanted to change the "flavour" of a game - make it into a completely new game, an offshoot of the main game. Take out all of the elements that make GC2 a slow-paced, relaxed (relatively), turn-based game and make "Galactic Battles" (or some less cheesy name), using the GC style, but playing more like Total Annihilation or Command & Conquer. Have battle maps that include battles "out in space", battles "in orbit", and ground battles to represent planetary invasions.
Have you ever played the Total Annihilation campaign? That basic core idea of going from planet to planet through galactic gates was amazing. GB could have more of a "conquer the galaxy" feel, by making you have to progress through conquering the galaxy in a series of space, orbital and surface battles. This sort of fast-paced game would be ideal for creating a MP/RTS game in the GC "universe", while turn-based GC would not lose what makes it great.
In the long-term, there might even be room for a FPS game based on the Q4 engine or something like that, where the maps/missions would involve shipboard combat, espionage (BE the agent who sneaks aboard a Drengi starship and steals the key research for the Phasor technology), rescue (save the captured Torian diplomat in-transit to the Yor homeworld for interrogation), and so on.
Heck, integrate it all - make it so you can click on an icon in the GC game and "jump" over to the RTS game to "play" the invasion of the Drengi homeworld (of course, you'd have to own both games).
