I think Dean's going to cure his fear of flying and get his pilot's license. He's going to needle Sam about stealing an F-15 at every opportunity (you need these things to fight ghosts). They're going to have an airy rickety house out in the Indiana Dunes or in Belgrade, Maine (shout outs to castiel, and Dean will trip over all the books Sam keeps. There will be two dogs, Newfoundlands, one named Pharaoh and the other Rosie (oh yeah, the ac/dc references keep coming), and they go hunting with them.
Dean will refuse to do the laundry always, and Sam will purposely mismatch his socks to get him back. There will be lazy sex and blowy curtains and maybe a hammock. Dean will start collecting vinyl now that he has a safe place to keep it, and Sam hooks up a soundsystem for him so he can blast away.
Sam in the mean time will build up a Monty Python collection, start a running club, and run around in a fuzzy robe billed in the catalogue as "the cloud."
What about you?