I think Walt is going to go out in a blaze of glory confrontation with the authorities. The writers of this series seem to love using foreshadowing and watching an episode of season 5, the one where Walt bought the new cars, got me thinking. He and Junior were watching the famous "Say hello to my little friend" scene in Scarface and Walt was totally into it. Now the 'peek into the future' scenes show Walt with a massive gun and ammo in the back of the Cadillac. Maybe it's just a coincidence but I'm thinking Walt is going to use the Ricin on himself (maybe a face full of it, in another hat tip to Scarface), just to be sure he doesn't last long, then he goes to town on those trying to bring him to justice. After all, he's dying and has nothing to lose anyway.