I'd be very happy if the new game was just an improvement on what Combat Mission has always been. I just want to see the game with more units, more options, better graphics and sound, just more of everything that makes the game fun to play.
I think going to a different era would be a mistake, since CM has always been about WW2. Regardless though, I'm sure it will be a good game. The last 3 have been great, and I expect we'll see even better things as the new game comes along.