This type of thing has been considered a number of times in the past—and, in fact, is still being considered.
However, it is a change that will require a huge amount of work just to make the code continue to do what is expected, let alone add the extra behaviour that makes it desirable, so...it's not something that we can just bang out in an hour or so.
What if it wasn't truly 2d but just three lines of the existing 1D map. In line settings you would choose "Center, Left Flank, Right Flank" along with the existing front, middle, back and rearguard. The units in different lines don't directly interact or fight each other as that would be too complicated, but if one side takes a whole line whatever lines are adjacent to it take penalties and have an ever increasing risk of retreat.
