The federal government is going to step in and start confiscating grow-ops in Colorado and Washington State. They will bust people doors down and most likely injure or kill a few. It's going to happen. The powers at the federal level are just too great.
It will be interesting to see what happens; the federal agencies are between a rock and a hard place. While the initiatives passed at around 55%, the polls for the feds to respect state law are over 70%. If they go after the industry as a whole, they would end up losing a lot of political capital among the "law and order" voters who otherwise support the drug war.
Note that the medical operations have dealt with a handful of nasty busts under Holder/Obama, but don't seem to be closing up shop or going underground. Drive down the right streets in Denver, and you'll pass literally a dozen legal pot shops operating in the open, neon signs and all.
I don't think the federal government is interested in getting into what would essentially be a pissing contest. They will just ignore the problem and let things be, because that is their prerogative (state jurisdiction!) and they have nothing to gain, only resentment, for getting involved.
Why aren't federal drug laws don't change because many of the other states won't let them. A lot of southern states are not so open about drugs. This isn't the federal government vs. a few states, its more like many states against many states; there is just a general disagreement in our culture like there was/is about gay marriage.
