Let me ask the obvious question here -- why in God's name do you need a cryptocurrency to pay for marijuana, when it's legal? Why not just pay for it with fiat? You'd think the essence of marijuana cryptos would be to keep transactions under the radar. What is the point of a "weed" coin once it's legal?
Is it just so the pot heads can feel like they have some grip on, or portion of the crypto community? You can toke up, play video games, eat cheetos, and proclaim your blockchain prowess!
I don't get it.
I think one important thing to note is that even though marijuana may have been legalized by the state, it is still illegal on the federal level (at least in the US). There are plenty of web-based businesses in the marijuana industry that can't necessarily work with cash, and the hazy state of legality may put a number of people off from using credit/debit so cryptocurrency fills that gap nicely. So while it may not be completely necessary, I think it's a good layer of security for something that's still possibly very risky.
Also, a few of the weed coins are setting up platforms for marijuana businesses that get shunned by more "mainstream" platforms. They can't advertise with Google or Facebook, so DopeCoin's Smoke Exchange could be a great option for them.
Actually the problem is banking. Most banks, being national and not state based, are unwilling to risk working with dispensaries (even medical ones) right now, which has resulted in most dispensaries becoming cash only as POS became impossible, especially once Square started refusing to process indirectly. Here in Oregon, that all happened right around the time Sessions took office (shocking, I know). Altcoins, specifically DASH, could solve the problem (google "alt thirty six" if you're interested in specifics). I know the weed named coins want to be that coin, and in some markets I think they are established to some degree--or it's all marketing and nobody is--but either way my money is on DASH to take on that role, at least initially, as the alt36 people have been setting up a POS system and trying to make agreements for over a year now (unless that is also marketing). However, in the log term, I think any stable coin with a fast confirmation cycle can easily take on that role...