formation of units into divisions, corps, and armies
These are possible including new army creation for inactive leaders, except for division formation, as inactive leaders can only take on one brigade/unit, which seems a bit anomalous.
It would be good to see inactive leaders able to form divisions but might give an advantage to the Union as the game is now organised, as they have hordes of 1* generals. Playing the CSA I've found a limit in forming new divisions is the sheer lack of officers, a limit for the Union being the lack of active officers.
It also deters the Union from building Corps "dream teams" of highly effective officers, the Union having to take whatever is going at the time.
Maybe if the CSA had some more generic 1* generals and there was a VP penalty for failing to give 1* leaders commands in order of seniority, it might redress the potential imbalance.
Might also be fun to add a few defective attributes to non-promotable 1* generals to make division and Corps formation a bit more patchy.
But, as little of this would be moddable...