This is the view of one private attorney, and one that has not been tested in any court and is definitely a minority view. I would be highly skeptical of his opinion (and I am surprised this attorney was willing to attach his name to it publicly).
The author's argument is that medical marijuana related activities are no longer subject to federal law. This sounds a little dubious on its face, but maybe it is a compelling argument.
This doesn't argue that possession is legal everywhere. It specifically talks about Nebraska, one of the states in the lawsuit:
""In states where voters have not voted on it, for instance Nebraska, of course it's not going to be legal there," Pappas told us. "But patients and medical marijuana centers operating in full compliance with state laws -- through equal protection -- are not going to be subject to federal prohibition.""
This is essentially the current status quo. The author's argument would only apply in the case where a future president acted to enforce federal statues in states where medical marijuna is legal. Then this arguement could be tested in court.
In theory, yes. In practice so few people are getting charged with personal possession under federal laws that a challenge is unlikely to happen before marijuana gets rescheduled.