I suspect that the states themselves will de-criminalize before the feds actually move. It would be nice, however, if they could reduce the status of marijuana. How about allowing banks to deal with sellers and growers for starters. Then reduce the status of marijuana as I think, by now, all the stuff about addiction, teen-age dependency, etc. have been flat out proven wrong. Its even better than that. When de-criminalization has taken place teen age has actually gone down!
A story. In Finland, I think, they de-criminalized marijuana. They did this because they knew that when teenagers drink they drive and when they drive they hurt others. They also didn't believe that folks doing marijuana don't actually get in their cars and drive. What happened is that they removed the thrill of sneaking something illegal and the teenager use of marijuana actually went down! (there is some indication the same thing is happening where they legalized)
drugpolicy.org probably has a lot more info on this stuff.