Just because this has been running through my brain and I want to bounce it off other people.
I'm beginning to seriously think that Sam isn't going to turn out to be the problem everyone's afraid he's going to be. I think this for a few different reasons.
1. It's too obvious. Now, Kripke has been known to use a few tried-and-true formulas within episodes before - Dean's personal "It's a Wonderful Life" and Sam's personal "Groundhog Day" (two of my favorites) among them. But as far as the larger story arcs go? Not so much. He leads us down one path, which we follow along happily, but then at the last second, he grabs us and pulls us in a different direction entirely.
I mean, really, did anyone see that semi coming before the headlights showed up in John's window? Seriously?
So, since we've spent the past two and a half seasons being told that Sam has this tainted blood in him, that he's going to go darkside, that Dean's going to have to choose between saving Sam and saving the rest of the world... I'm fairly convinced that none of that is going to happen.
2. Wherever these two go, they're going there together. If they march into Hell, they're going there to kill some evil sons of bitches. If they march into Heaven, it's as triumphant warriors. If they stay on Earth, it's as Hunters. They canonically cannot exist without each other; they love each other that damned much. And call me crazy, but I just honestly don't see them spending all this time and effort establishing this amazing, co-dependent, crazy-as-all-hell brotherhood these two have going on... just to chuck it all in the toilet and leave us with one ruling Hell and the other commanding Heaven. So this is the hopeful part of me that says, "Never gonna happen."
So, what do I think is gonna happen? Honestly?
Right now, I'm thinking that Uriel and Lilith are gonna join up. Think about it: Uriel is one of the seven Archangels charged with ruling Earth after the apocalypse. He's an angel of vengeance (which means he has a temper from Hell, if you'll pardon the pun). He's been promised Earth since before time began, and now all that's standing between him and it are these two measly, insignificant little... what'd he call them? Mudmonkeys?
Think about that, folks. A racist angel? Really not a good sign.
So Lilith is breaking the seals, right? When she's done with them, the Gates of Hell will open and Lucifer himself will walk on Earth. Armageddon.
Now, who would be more inclined to stop her? The angel charged with defending/preserving the soul of at least one of those "mudmonkeys", or the angel who's waiting for the apocalypse to happen so he can inherit "his" planet? Conversely, which one would be more inclined to help her?
So that's my current speculation. Anybody else have any?