Sorry, I guess I didn't make my daydreaming very clear. In AW, you could get different skins just for terrains (separately from plane skins), so that each player could change how an arena looked to him simply by choosing (for example) default, desert, winter etc., just like choosing a plane skin.
Of course, the terrains were rather "primitive" in the sense that the trees were very sparse and crappy looking, so it made those skins much easier to do in AW than they would be in AH. Probably AH also uses different methods for building terrains than were used by AW, so that would complicate matters a whole lot.
But I can dream, can't I? It will be so kewl to see a winter terrain in the Allies vs Axis. I plan to die in there all next week.