As GC3 is the first multiplayer GC incarnation, it's crucial to switch to a multiplayer-friendly game model, rather than sticking with the traditional turn based model where people wait for each other to finish.

For the perfect multiplayer experience, the model needs to support the following:

• Game hosted on central server at Stardock
• Player can create new game, control turn deadlines (10 minutes? 2 days?) and pause game, ie. for when vacations get in the way
• Players will plan their actions and submit their turn. Once turn deadline has been reached a new turn is calculated with all player actions being carried out simultaneously (ie. noone "goes first")
• Players need not be online at the same time. Turns can be planned and submitted individually.
• Game scales without adding delay, ie. whether you're just 2 players, 50 or more the delay is the same.
• Players missing turn deadlines or dropping out wont halt the game.
• Long term planning (order queue). Unfinished orders, ie. long flights, carry over to next turn.

Stars! employed a fairly similar simultaneous turn based model, although without a central Internet host.

I believe Endless Space does too to some extent, although as far as I know it does requires all players to be online at the same time.