Kalalokki
Sprite Leader
There is a metagame called just that made here on Smogon, but with a bit other rules than what you suggested, and it was playable a few months back. http://www.smogon.com/forums/threads/stat-switch-azumarill-regice-banned.3518568/I would like to see a tier called "Stat Switch" come to Pokemon showdown where all the stats are switched with its counterpart.
HP <---> Speed
Atk <---> SpA
Def <---> SpD