This sort of move is to be expected and it will be fascinating to watch it play out. I just read an interesting article about how the shops legally selling weed in Colorado can't get bank accounts (due to state and federal regulations) so they deal with huge amounts of cash and have to hire specialist security teams etc. Obviously using bitcoins is a perfect way to avoid all of that hassle.
Sad this is I just read on coinbdesk that payment processors like bitpay are refusing to work with marijuana related merchants in legal states due to current federal laws. They are already walking a fine line with banks by dealing with bitcoin so they don't want to step on any more toes and start getting involved with merchants who are breaking federal laws.
Of course pot stores can still accept bitcoin on their own without any payment providers but then that makes them liable to the volatility of losing bitcoin and it starts become an unsafe/unsmart business practice to accept funds that can/will drop in value at any given moment (or increase in value).