I concur with the thought of having two units per hex. Most tactical hex wargames use or used this rule. One main point for this, is for helping with unit congestion, another is the ability to reinforce a battered unit. Some other important factors are the ability to strengthen a vulnerable portion of your line, or place a tough double stack in reserve. The options are endless. This idea would add flavor and fun to the combat aspect of the game. I also agree it would help the AI immensely.
I disagree with using unlimited stacking with a hex map, to me it would make no sense. What would make sense in respect to hex warfare, is unit facing. The direction a unit attacks or defends from, or gets attacked from, should be a big part of the tactical strategy. If a unit gets attacked from the rear or flank there should be a combat penalty against that unit. Of course with unit facing rules put in place, there would have to be rules put in place for retreat, and rules put in place with regards to zone of control. In the meantime 2 units per hex would be an important big step in making this game better.