What to add -
1} better and more terrain types. you should be able to "paint" in a line of trees for example. not block in a patch of them, for more flexability in the map editor. the same thing could be applied to fortifications such as trench lines and barbed wire. instead of painstakingly placing one at a time inplace, you could paint a line across the map in the editor to save vast amounts of time.
2} A grand campaign system where you start out with a core set of units and upgrade them as the fighting continues. id love to see the units elligable for promotions and medals/awards.
3} A Pacific version. i cant tell you how bad i want to assault Iwo Jima in Combat Mission!
4} I know the new versions will be more battle specific. that opens the door for the opportunity for you guys to use more rarer AFV's/vehicles/airpower/units/ect... that werent included in the game. such as schmalturn Panther turrets in the italian moutain fortifications and German festung citys. or the German nebelwerfer halftracks that were used in the late war, just to name a few.
5} And last but certainly not least, and i cant stress this point enough, MULTIPLAYER!
What to keep -
1} WEGO system.
2} Simple map/scenario editor.
3} Easily modded game graphics.
4} PBEM.
5} Fog of war, i love that, it makes it more realistic.