OK, Friday everything I write right now may be obsolete, but I can’t help myself speculating about Cas and Crowley.
I think it used to be that way: Good people go to Heaven. Bad people go to Hell. Some people become monsters and go to Purgatory. Few people sell their souls and go to Hell too. That was the natural order. Heaven, Hell and Purgatory use souls for some kind of energy. And now because the apocalypse was prevented everything is a mess.
Why did the Cas/Crowley cooperation start?
Instead of a Heaven/Hell/Purgatory triangle (even if we didn’t know about the latter) there is Heaven, Hell, Purgatory, Crowley and Cas.
Cas was all of a sudden the “new Sheriff” in town and had to fight a war against the other angels who followed Raphael. Apparently Raphael had access to the power of the souls in Heaven but not Castiel because he was losing the war. So he had to find another way to win the war, meaning having access to souls. Crowley was probably in a similar situation. We know, even with Lucifer in the cage not all demons followed Crowley. He complained about that so he had like Castiel a kind of civil war going on. Cas and Crowley knew each other; they had similar problems so it would have been logical to work together.
When did the Cas/Crowley cooperation start?
I guess right after “Swan Song” because that was when we the civil war in Heaven started, from this point on there where new players involved.
Not too long ago Cas was a good, proud angel of the Lord. Then he met the Winchesters. Under their influence he learned to think for himself and making own decisions. He rebelled against heaven but not against God because God brought him back at least twice. So God probably liked what Cas was doing. Cas learned to make his own decisions but who says he made the right ones.
Clearly we have to doubt a lot what we learned this season from Cas and Crowley. I’m thinking about the monster prison from “Caged Heat” and Sam’s soul and how Cas and Crowley agreed on not returning it to Sam. Balthazar’s “helpful tip” about tainting Sam’s body with patricide could have been on Cas’ behalf. Even Cas being furious about Balthazar buying souls seems different now. I think Sam’s soul was in the cage (we saw it when the wall came down) but maybe not for the whole time.
As long we had SoullessSam wandering around Dean was kept busy with collecting monsters and worrying about Sam and SoullessSam didn’t care about anything.
In the preview we hear Cas praying to God witch is the smartest thing he can do, but probably not helpful.
Time for some speculations: What if Crowley and Cas together got Sam out of the cage and Crowley left on purpose Sam’s soul behind? Cas got Grandpa out of Heaven to team up with Sam. They go fetching monsters to find out where Purgatory is so Cas and Crowley can get the monster souls. This all brings up MOA and also upsets Death and the natural order.
Don’t forget Crowley and Cas were not successful because by now they couldn’t get their hands on Purgatory and the souls in there. So Cas is very desperate and sends Balthazar back in time to unsink the Titanic with the known result. Right now Cas must be desperately in need for energy/souls to win the war
In the preview Cas says they will die over and over again if this would be Star Trek, I would guess a time loop, but I don’t think Supernatural will go there.