They rarely IF EVER have the arena's locked in for any show more than a Year ahead of time... the closest to this was when Summer Slam spend 5? years in California... you could guess it'd be in southern CA but they didn't pick a Venue until the date approached... and now they've stopped this practice
Heck, I'd imagine most Raw/SD! taping sites aren't picked more than 6 months ahead...
The three places I've read putting in the most significant bids so far are Orlando, Philadelphia, and Minneapolis. I'm thinking it will be either Minneapolis or Orlado if it's one of those three. A city I think would be good for a WrestleMania is Nashville.
Imginationland
Papua New Guinea.
They havent announced it or probably even thought of it yet
WWE hasn't said yet.