I think the Grey Matter scene is motivational for Walt, but not to do something against them. Remember that this whole series started with Walt cut out of the millions that were rightfully his. And remember that a lot of his motivation right from the start wasn’t just to care for his family but to “get what’s mine”, i.e., recoup his losses from Grey Matter. Then throughout the series through his meth-making enterprises he builds an empire and is eventually richer than his former partners (recall that during the Charlie Rose segment the Schwartzes were throwing around figures like $23 million, small potatoes next to Walt’s $80 million+) Having beaten his colleagues at their own game, it looked like Walt was going to semi-retire and be satisfied with what he’d got.
Then Hank had to figure out who he was, and the shit hit the fan. As a consequence, Walt loses almost all of his fortune, and the comfortable life the Schwartzes enjoy. I think in the cabin in New Hampshire, with Walt getting significantly sicker, he was probably thinking, "OK, I’m just going to die here, but I’ll try to at least do one of the things I wanted to do from the start, I’ll send my family a little bit of cash, enough to keep them eating. Then he gets blindsided by Jr.'s tirade against him and he realizes he’s lost his family anyway. Jr. hates him, Skyler would flip on him if she could. If he wants to save his family, all he’s got left to trade is himself. He’ll reinforce their innocence and probably die before the trial. So he calls the DEA, sits down with a double, and waits for them to get him.
But then he sees those smug asshole Schwartzes on TV and remembers, hey, I had other fish to fry here. He’d talked to Vacuum Cleaner Guy about getting his money back from the Nazis. I had an empire, damn it, and those Nazis took it away from me just like the Schwartzes (heh heh, Sgt. Schwartz) did. Walt doesn’t have much time left. You’ve got to think, cripes Walt, even with your machine gun and vial of ricin you have no chance against an armed compound full of Nazi toughs. But Walt’s got nothing to lose. Todd, who I agree seems to be their leader by dint of having two brain cells to rub together and by his recent demonstration of being a cold blooded psychopath, has everything to lose: the recipe, Lydia, and most of all his budding empire. The scene is set for a showdown.
My wild-ass prediction for the final scene: Walt shows up at the Nazi hangout armed for bear and kills the Nazis. He sees a suspcious-looking tarp, thinks the money is under there–it’s Jesse’s cell. Jesse begs Walt to kill him, they’ve already killed Andrea and they’re going to kill Brock any day now, I’ve got nothing left to live for. Walt thanks him for everything, throws in the ricin, and re-covers the cell. One last showdown. Walt breaks into Todd’s lab. Todd tells him, I’ve always respected you, I’m halfway to building the empire you always wanted, let’s go into business together. Walt answers with a bullet. In the corner are several familiar barrels. Walt opens one and it’s full of cash. He’s got what he wanted. The camera focuses on the cash. We hear coughing and blood spilling onto the money. Fade to black.