i agree-- it's anvilicious. after ruby leading sam around by the nose in order to manipulate him into place, this idea that there was a whole endgame involving the special kid champion has been taking form for a few seasons--as a vessel for lucifer is the next logical place to go. which is why i hope against hope that it's a fakeout.
and that next season isn't michael!dean killing dragondevil!sam but rather WINCHESTERS & Co versus EVERONE SUPERNATURAL-- I'M LOOKING AT YOU CREEPY ANGEL DUDES!!!