Here's one from left field: every theory about the ending supposes that Hank's going to do the lawful thing. What if he finds out about the White's heowge stack o' bills and offers to not bring the law down in exchange for 50% of the money?
After all, they've made a bit of a show of his increasing disillusionment with DEA upper career rungs - wistfully reminiscing about his tree-marking job, for instance - so maybe he could be swayed by a Walt-bargain along the lines of "Here's half the money. I promise that my law-breaking days are behind me; we can both retire and give our families the lives we've always dreamed of. Whaddya say, Hank?"
He is, after all, the only one at the DEA with a sniff of the blue meth trail. Hank goes quiet, the trail dies. Hank brings Walt to justice, however, and it's "How can you expect to be respected within the DEA when your brother-in-law was Heisenberg? GTFO etc".
Not sure how it would tie in with the flashforward at the start of the season, admittedly, but I think with Gilligan it'd be naive to assume that it has to be Walt v Hank & the DEA...