A MP campaign is impossible with the current engine, someone from CA told that once. I believe it was BOFH or Pras

Anyway it's impossible anyway:
21 players
everyone takes atleast 10 minutes to make his turn, maybe even 15.
At average everyone attacks once in his turn. Each battle takes 30 minutes atleast.
Sometimes you have to wait for other to go to toilet and such, maybe eat dinner. Let's say that's a total of 2 hours.
Add everything together
Battles = 30 x 21 = 630
Turns = 21 x 10 = 210
Waiting, etc = 120 = 120
that's 960 minutes, which is equal to 16 hours.
And that's turn 1.
So you sleep 8 hours, play 16 hours and have no life.