I think this is a good idea. Not because I think it's good policy, but because the current situation is ridiculous and promotes the uneven application of law. I don't believe federal possession statutes are constitutional, and even if they were I don't think they're good policy, but laws should either be enforced or struck from the books.
The breadth and depth of federal law and regulation itself supports the uneven application. Those who have money can find a lawyer. The remainder of us are chattel kept only for cleaning the toilets of the wealthy.
If the breadth and depth of federal law and regulation supports uneven application, the solution is to pare back the breadth and depth of federal law and regulation, not pick and choose which laws you're going to enforce. The latter leads to a situation where all sorts of draconian laws are passed and nobody cares because they don't expect those laws to be appllied to them.
But that gives the government all the tools it needs to make life a living hell for people who irritate the mandarins in Washinton. I'd be curious to know just how many people in federal prison for possessing less than an ounce of pot are really there for possessing less than an ounce of pot.