They definitely mentioned 4 player co-op before, though I don't remember where.
It was earlier said that there would be the 2 main characters and then the other 2 players could control their henchmen. So they wouldn't get to make their own characters, but they could still play.
This changed somewhere down the line I believe, but still in the early days.
Now they say you can still play with 4 players (maybe even up to 6) but only in custom campaigns. It may be possible that the original plan of having the other 2 players control henchmen will be modded in.
