No surprises here really. It's illegal under federal law [pdf] and that's the end of it as far as ATF is concerned. Furthermore in that the feds are the least accountable of the many layers of government we are afflicted with that is indeed that. Congress isn't going touch this issue with a ten foot pole and neither is the administration so unless ATF relents or some federal judge engages in some "judicial activism" this door is shut tight.
My advice to shooters that like to get high is this: Just grow your own, be discreet about it, and leave the feds the hell out of it. What this portends for local stoners with guns around here (especially those with Michigan-issued CPLs) is uncertain. What is certain, at least to me, is that no amount of permits, licenses, and permissions slips from the bureaucracy is ever going make you free.