My guess would be that by the president pardoning these crimes, it would potentially make it more acceptable for governors to do the same for state level crimes.
However, it still doesn't solve the overarching issue of draconian drug laws.
Ia that really ironic though? If anything, it should be something we value. Granted, this was much later than would have been liked, like decades later. But a politician going, "oh, wait, that policy I helped passed turned out to have bad side effects. I see it now, recognize it and will do something about it." We have too many politicians who pass bad policy, and better yet pass it, watch it blow up in their faces and move on with their life to never revisit again. Chances are, most to all politicians are at some point going to pass bad policy, the important part is, recognizing when things go off the rails and correcting course.
However, it still doesn't solve the overarching issue of draconian drug laws.