the ricin has to be the climax of the show. walt is going to poson someone very powerful, maybe a bad guy gonna hurt skyler, and a gun just won't do it.
Maybe he will do what gustavo did... bring a drink laced with poison, and both he and all the bad guys after him will die together? Maybe a scarface kind of ending? The writer talked this week about his love of scarface, and there were lots of references in the season 5 (shown earlier this year) to scarface. Ends will probably parallel.
I think they'll kill off jesse. He's useless as the "retired meth maker" and will just be more of what he is now, whiny, etc. HE was the actor that said it would be a bloodbath - so I think he'd going to die. IMAGINE that episode... jessee dying in walt's arms, after taking a bullet meant for him or whatever. Then walt puts the kids in safety with hank, hits the road, and does whatever he needs to do. The show will HAVE to introduce some bad guy in the next episode or 2, that will be walt's big target in the end.