Shroomy
Adventurer
If it were a new setting, I'd bet on Rich Burlew's or Phillip Nathan-Toomey's - the runners-up in Wizard's setting search. WotC still owns publishing rights to both; I don't see why, if they needed a new setting, they wouldn't choose one of those and start working it into a 4e setting.
Didn't WotC already incorporate parts of those settings into Eberron itself. I swore that I read somewhere that ideas behind Aerenal were taken from Rich Burlew's setting pitch. Maybe I'm misremembering.
I voted Dark Sun, but I wouldn't be suprised if it is Dragonlance or Greyhawk.