Washington State started allowing legal recreational marijuana sales July 7, 2014. Prices were high, supplies were low, and lines were long. The roll-out was smooth, with the main issue being a lack of inventory. In the case of Seattle's Cannabis City, supplies lasted half a week, forcing the store to close until July 25th or so. Despite supply shortages and closures, the State of Washington was still able to generate quite a bit of tax revenue. Per the Seattle Times:
Washington state will add more than $318,000 to its coffers as a result of 10 days of legal retail marijuana sales, according to figures provided by the state's Liquor Control Board.
That number reflects $1.27 million in sales throughout the supply chain, including those from suppliers to retailers, but does not account for sales tax or business and occupation (B&O) taxes.
If that's what the state was able to generate in just ten days, and with only a handful of stores open, and considering those stores had to deal with supply issues, I'd say that the future of marijuana tax revenue generation in Washington is only going to get better. I'm curious to see what the numbers are like when every customer that wants to buy legal marijuana can. This of course would involve all stores that qualified for a license opening, and staying open with adequate supplies from all of the growers being in full production.
In February the Washington State Economics and Revenue Forecast Council estimated that Washington State would bring in $586 million from marijuana taxes between 2015-2019. I think that if the industry was firing on all cylinders, and that all stores, growers, and processors that qualified for a license were able to operate unimpeded, the State of Washington would far exceed the revenue forecast. With 25% taxes at every step of the way, and the amount of demand that is clearly out there, I don't think exceeding the revenue forecast would be that hard to do in one year, let alone during a five year period. I guess only time will tell.