You know, if we do get an Arcadia AP, I really hope it's not a kingdom building AP. Not just for the really good reasons listed above, but because we've already done a kingdom building in a wilderness region, I say we go nuts with it if it ever gets revisited, outer planes, First World, the Underdark (although that might be stepping on the new Fire Mountain Games AP).
Maybe the group is one of those poor mortals who don't know they're stuck in the Abyss or Abaddon who figure out the horrible truth and try to carve out a safe region for themselves. Or maybe they have to go to the First world and wind up becoming masters of a small region there, where the land itself reshapes according to their desires.
But my personal favorite would be Kingdom Building involving the Land of the Linnorm Kings. Building a settlement, making alliances and enemies with your neighbors, dealing with mysterious fey, and finally fighting a Linnorm to seal your right to rule.