I wonder how much effort it would be to create a "Planetary Annihilation Classic Edition" with flat maps. I suppose parts of the engine and most of the assets could be reused. You could even have an orbital layer and multiple "planets" in the form of disconnected parts on the map only accessible by "space travel". Only the smashing and planet lasering probably would need some rethinking The game would likely be more accessible for beginners and less demanding w.r.t. the hardware requirements. I know, it's heresy, but I actually think there would be a substantial market for it...
You aren't the first person to request this, and you won't be the last. While I'd play on spheres most of the time, I'd love to be able to change it up and play on flat maps. Uber has said this would moddable, so it'll happen eventually. In theory. Any updates from modders on this happening?
I would be more interested in scenarios where you're limited to a particular section of a planet. E.g. Restricting play to one hemisphere of a planet, or to the equatorial belt (as with metal planets, but air/orbital can't travel over the poles).