Although it's possible, I find it highly unlikely they would completely change the theater for an expansion pack (otherwise they would have done it for COH1). I am hoping they expand on the Eastern Front a bit by adding minor factions like the Finns, Hungarians, Italians and Romanians. Also, it sounds like for the campaign they plan to go from 1941 to 1945. I am not sure if that carries over into multi-player, but something they could do is add a drop down menu for time periods and each expansion or DLC could add new units for different time periods - kind of like the modern day equivalent to tech levels.
I also hope that terrain is factored into projectile trajectory. It would be nice if cannons no longer shot through hills and such.
From the pictures it looks like the SU-76M is properly scaled, so they seem to have learned that lesson.