I really dig this idea too (nicely presented Golden_Ace!) and it's no surprise Moon was one of my choices on the new zones survey.
Here's my moon-thoughts from that thread
As a side note to my choice of the Moon. I really want to be able to go out onto the surface, either for missions or for street-sweeping (maybe the Rikti have a moonbase, or Arachnos, or Crey, etc,. Or maybe they ALL do

).
Imagine white/grey craters and hills as far as the eye can see, moon bases for the various factions, an Apollo landing site would be awesome if not on the main map then maybe an instanced mission.
Imagine looking up to a black sky with the Earth in place of the moon, but larger and the sun blazing bright above. There could even be missions or a sub-zone on the dark side, where it would be pitch black but with a impressive star-filled sky above to just give enough light to make out things close at hand (kind of like DA).
I was trying to come up with a solution to how this could be done as far as explaining heroes and/or villains hopping about outside.
I think all that would need to be done is in the same issue it became open, provide an assortment of spacesuit costume options for those who's background or character concept wouldn't support a "I don't need to breathe" style like Firelord or the Silver Surfer.
At first I thought you could make the suit something like a temp power (like the backpack for fighting fires in SC) but by doing that you end up with a one-style-fits-all look that would make it impossible to discern who was who except by looking at the name above their heads.
But with cool spacesuit costume options, it would make it your choice and the suit could have your characters colors and styles (i.e. Batman's spacesuit would still look like Batman).
The only other problem I forsee is the physics. Imagine Knockback on the Moon. Can you say "Seeya!"?

This could be quite entertaining, especially with ragdoll physics, seeing a mob flail around in slow-motion until he bounces a few times 100ft away. However, this could become quite a headache, if not to program, then to play around with.
Try tanking a group that your team's energy blaster is tossing for a 50yrd loss.