I'm thinking the current medicinal shops do pay a tax. At least within Denver.
There is nothing to stop these shops from having a walk in and buy program either. Most if not all will probably stay as medicinal and wait to see how this works through the courts.
The Feds are probably going to challenge this big time. They know that if they don't make a show of it, during the mid terms, there will probably be a fair number of states that join in on this party.
The next year or two should be fun to watch.