Generating Novel Battle Maps
From giving the players the editing tools necessary to create their own maps, this idea may already have occurred/is being implemented in the near future. However if it is not, I want to say that the development of new maps for neutral/PvP battles would be a good near-term goal.
Fighting on the exact same map over and over again gets a bit tedious, very quickly. With terrain of all types to explore and potentially exploit (I hope there will be terrain/weather specific effects on units sometime in the future to consider), it would be a shame to limit players to just a handful of maps to play on.
I think it could be solved by either a lot of effort by the developers to make tons of little maps and detract from their efforts to otherwise improve/build on the game, OR the more fun way would be to have the community, already very enthusiastic and eager, to make most of them.
Having a few community contests for the best maps for whatever region would steadily increase the number of maps available for all players to play on. Then when a player was in a certain region and ran into a battle, they could have the chance to play on Map A, B, C, D, E... and so on for however many maps existed for that area. Definitely would increase the long-term interest of players to not only play the game for varied battles, but also involve the community in the making of significant parts of the game - freeing up developer hands and giving the players something else to get excited about.
It would be up to the developers to choose which maps worked, as any obvious imbalances in terrain or nonsensical doodad choices would have to be considered (like a cactus in a swamp or whatever), but I bet the players can make and perhaps have already made really awesome maps that should be in the game for everyone to enjoy. And the only part aside from implementing an easy system of loading in new maps and placing them in the game for the developers would be to give the thumbs up to those maps.
Also: This idea could apply to Player City maps too, since I move that there be a lot more variation there especially for players to navigate.