Why not? Pretty much every decision Square has made either blew our mind or moved up a world we'd thought would be in a later game. It would be the one world to actually make sense, not to mention that having two Wonderlands in the same realm would be totally weird and it belongs in the Realm of Sleep more than anywhere else. Besides, wouldn't this make a GREAT boss?
http://t3.gstatic.com/images?q=tbn:ANd9GcSmUo2OONIAeESBRg2rWizTnCsg_1fVW2TSTfxbdpMJAcL2B3cr
http://images2.wikia.nocookie.net/__cb20101118002337/villains/images/thumb/d/d0/Jabberwocky.jpg/300px-Jabberwocky.jpg
Also, we'd have new villains like this and the Red Queen and we could actually meet the Mad Hatter this time, instead of being sealed in a painting for some weird reason...