I know where you are coming from but I think there are competing factions within the Feds. For instance, everyone is focused in the DEA while the DEA is actually looking to the FDA for guidance. Here is what would need to happen:
“Ultimately, we want to see the FDA approve marijuana as a legal prescription drug,” says Brad Burge, MAPS director of marketing and communications.
For that to happen, the FDA would have to approve marijuana for a specific indication, based on scientific proof that botanical marijuana is safe for human consumption and that it does, in fact, yield medical benefits. If this study is successful, Burge hopes more research will follow to determine which strains are most useful to address certain symptoms, what dosages are appropriate, and best methods of delivery.
Also, consider the insane amount of tax revenue they could collect if they taxed it federally. I haven't heard any news of mass layoffs of cops or anyone for that matter in Colorado. They are swimming in dough. As long as the Feds can calculate a profit, they will go in that direction. I think they are seeing dollar signs in legalization.
News 
Market Data 
Discover 
