Hi there,
no I think, human Players wouldn't leave a game, when they have enough to do in their turn ... so the waiting time, that they could do anything, should be as short as possible.
I am playing only with friends MP , so our MP games are somehow more COOP against AI, but not really coop ... everyone is looking to achieve as many Points as possible 
The worst time is, when the AI is taking his turn ,,, special if we play Civilization V
SO IT SHOULD BE ALWAYS THAT ALL PLAYERS PLAYING AT THE SAME TIME , and even when I have pressed the Button "NEXT TURN" .. I should be able to plan already the next turn ... examine the map, looking for trading Partners, looking with whom I could trade and so on ...
some of that points are working in Civ V but MOST DON'T !
WHY EVERYTHING AT THE SAME TIME, it helps small nations and the AI , as Players with small Empires could do their turn optimal and have sometimes the advantage to do their important move , before a Player has done it, who already has dozen of other moves !
OF COURSE TIME LIMIT, which depends on the smallest player and or the fastest human player ... when the first human Player finished his turn, a clock starts to Count down to Zero, how Long depends at the state of the game !
I AND MY FRIENDS don't like that 30min to 4 hours games ... our CIV V games are most over 20-30 hours Long (3-5 meetings) ... 4-6 humans + 6-8 AI Nations ... but we would prefer 4-6 humans and over 40 AI nations (in CIV V 64 Empires would be technical possible ... )
AND TO SPEED THINGS UP, there should be a MULTITHREADING SERVER VERSION, which only needs a very fast CPU and near no GPU power at all, as only the clients should need high GPU power...
really loooking Forward for
- MULTHREADING SERVER VERSION
- Players and AI SIMULTAN TURNS (with or without timelimit)
- CLIENT could always do something between the turns
- up to 64 human or AI nations
- MOD Support for MP
PS: Gal CIV III is my first "founder supported game"