Well from personal experience any attempt to play the MTW2 campaign on-line in real-time mode is doomed to failure. When you might have a dozen people involved and a game which is going to take in excess of a 24 hours of game play to complete its just not practical.

So, in my opinion the way forward has to be PBEM. Let each player make their move in turn and pass the PBEM baton to the next. To make that easier would merely involve a system which allowed players email addresses to be logged with the game, so that as each player pressed the end turn button the game automatically posted the PBEM file to the next player in sequence, as well as generating any battle data files needed for the battle engine.