That's all hypothetical and we have an election coming up. And, it misses my point. That point is that you cannot have a true industry built on such "trust me. we won't arrest anyone, . . . today", ground. No respectable company, and by that I mean non-pinky, is going to touch MJ in a serious way until the legal implications are removed. There are no serious players in this market. They are all of the CANV variety, all of them skirting the law (in more than just the basic product).
I wish the feds would just abandon the whole "war on drugs" crap, too. It's a waste of time, money and other valuable resources.
They may be forced to, as you have hypothesized. But until then, all we've got are pundits and demagogues.
Bible presidents? GWB wasn't that long ago. Never underestimate those people.