Sorry for the double-post, but I figured I'd drop in before I went back to my spriting cave in order to let you know that this has been officially taken up as a project.
We have no information on the game name or anything really specific, and it will resemble Advance Wars in a great many ways, however, the twist to the system will be the addition of battlefield "layers".
So, not only will you have the topside battlefield as normal, you'll also have underground and sky battlefields.
And gaining the upper hand in either of those can do good things for you (dropping in more troops from the skies, or planting mines just below the battlefield surface, for example).
In some cases, there could even be multiple layers on either end (up to 3, maybe?), or no layers at all, making each battle diverse not only in terrain, but in the things you can do. You will almost never be able to use the same strategy for every battle you enter into, because the option you most often use will not always be available. I really think it'll make for an interesting system.
EDIT: My time in the spriting cave has yielded results. I'm still not happy with the way the helicopters look, but it's a step in the right direction, at least.

Any suggestions? I appreciate it.
EDIT II: I also tried my hand at an animation for one of the tanks. Any good? I feel like it needs improvement, but I'm not sure how.

EDIT III: Updated the OP with the latest full spritesheet, which has the beginnings of the map tilesets on it now. Enjoy, and critique anything here. I'd be happy to have your opinion.
EDIT IV: Updated the animation a bit, so that the treads actually move, plus there's some context of motion. Also gave me an excuse to test the tiles.