It would be nice if there was a little bonus when we attack a unit from two different directions at the same time. That would encourage real strategy rather than just "make a big stack and smash your enemy".

Also, if it were possible to retreat (even at a high cost), flanking would be much more appealing and the game would be much more strategic, like in a real war.

Also that option would benefit some units that aren't too much usefull like armored cars and light tanks (for their speed), militia (because they can be made o any province and engage an enemy invader from multiple directions) and obviously paratroopers.