I like to see more of the armored trains for each country, maybe they would have to be destroyed before taking a base after town is down or something like that just a thought.
If you searched then you would see that there was something simmilar asked for many times. We've asked for the factories, and refineries, etc, along with trains, barges, and convoys to be directly likned to the ammount of supps a base had. I know its not quite like your idea, but its simmelar in that it affects the ease or dificulty of base capture.