I like the idea of changing from all air to land, sea and air. I think that'll definitely add a lot to the game, because only having the three altitude things isn't really that interesting. All air would effectively be only on one plane, and that would get repetitive.
Adding in a ground layer also should synergize with the three altitude parts - ground units would have varying levels of range and most could only hit the lower altitude strata, a few could hit the middle altitude and one or two could hit the high-altitude air strata. Poof, instant strategic depth.
I definitely hope this means that all the base building is removed form the floating rocks and put onto the ground. I wasn't really a huge fan of that, especially the part where you have mines on the floating rocks.
