...They're gonna kill everyone and set Season 7 in Purgatory. This is the only acceptable answer, because they know that the reason their latest seasons have been so popular is Cas.

Also, the latest episodes make me feel like they're going to off Sam and Dean (again).

But yeah, the line whole new beginning? Season 7 could totally be set in Purgatory. It makes sense. But then, so does the Cas and Balthazar thing, but that's almost expected just because y'know, there are like no characters they can kill off because they already killed everyone off.