@MeatPopsicle:
touche, salesman.
Thankyewverahmuch~
Now for my own theory … I know it's insane ... but I think Blackbeard will eventually ally with Luffy. They have a lot in common, and while Blackbeard has done some pretty nasty things, the fact remains that the true enemy is the World Government/Marines. Also, Blackbeard is so far the only known enemy D ... and what we know about the D's so far really implies that most of them are good in the end.
Also, I expect this to be a controversial suggestion ... but I expect Smoker, possibly Tashiki to ally with the Straw Hats (possibly join, but I don't want it to go nearly that far). Simple thing is, Smoker is very strongly in support of "Moral Justice", and one of the most intelligent members of the marines. He must already realize that the World Government is corrupt; his view on justice, however, directs him to focus on the pirates. I see him eventually realizing that the good deeds the Straw Hats perform more than atone for their transgressions, and he's given the proverbial middle finger to his superiors in the past anyways. Pretty much the only thing against this is that Smoker is, by all accounts, the most invulnerable character in the entire series (how the hell do you fight SMOKE?!?! The man has no apparent weakness!), and therefore would make one rather interesting final boss ... but with that kind of morality, I don't expect him to actually fight Luffy to the death. I only mention Tashiki because, face it, she's a lost cause without her precious Smoker...