Air maps were some of the most enjoyable types from original Total Annihilation. Air maps were maps that existed on high cliffs where most things were unreachable without some kind of air support or transport. Does anybody remember these? Please don't forget Air Maps Uber! More pictures here! http://imgur.com/a/JbZxc
Where I don't see these maps being as prominent as they might have been, I can't imagine they'd be impossible with the world creator. Might take alot of tweaking. I've also raised an argument for having surface battles on gas planets being exactly that, only 0 solid ground, units and buildings would have to be hover/floating above the "surface" gas.
By the sounds of it, this is effectively what they seemed to be getting at when describing how combat on gas planets could be like.
However, gas giants described 'orbital' units, so not so much air maps as 'air maps without aircraft'. Which would be very nice. Volcanic planets can shape up as air maps, maybe.
I view Gas planet combat as where you build a Bespin style floating city in the orbital layer, then lower it into the upper atmosphere to harvest the [strike]Tibanna[/strike] Hydrogen gas for the city's super fusion plants, with some sort of laser transfer system to send that energy to an orbiting star base, which beams it to the rest of your system wide economy. And on these floating cities, you can build base defenses, aircraft factories, repair pads, etc. to serve as your base on the gas giant. I'd also like to see the cities able to move, if slowly, so that you could build a base defense heavy base and use it like a giant floating battleship, slowly moving from enemy city to enemy city and sinking them. Or load up on aircraft factories and use them as giant aircraft carriers. It'd be up to you.
Slate was a palette swap of lava (albeit a very visually appealing palette swap), so I don't think it'll be too terribly difficult to pull off something similar.