So basically, the original early adopters have it better than anyone now can ever hope to get. Not that we can't do well, but the gravy train has already pulled way out of the station.
No one can read the future. I like to envision a post-apocalyptic steampunk wasteland where holding a whole bitcoin is equivalent to being a millionaire. Let's meet back here in twenty years.
On a side note, how can draw any conjecture on the size of the 'underground drug economy'? Any number you come up with is complete BS speculation. I have never answered a poll about how much weed I sold last fiscal year, nor can I imagine that many other black market operators did so honestly. Any number that LE of governments throw about are extrapolations based on what they caught, which is impossible to calculate because they have no idea what percentage they missed...
I had a business partner with whom I designed and set up legal (usually) grow spaces in Los Angeles and the surrounding vicinity. Before embarking upon that venture, I had no idea how many lofts and warehouses in downtown were housing 20,000 square foot flowering spaces...and that is just what I have seen and worked on...only in LA. The real numbers have got to be exponentially higher. Only one garden I set up got raided out of dozens. Narcs seized about $50,000 worth of wet product out of a 600 square foot canopy space...and they thought they had made a find. 600<<<<<20,000. The proprietor walked after testimony from cannabis expert witnesses and 16 members of his collective.
I am no economist, but I know your model is oversimplified to the point of irrelevance. The vast majority of the world's wealth is not tied up in paper. I doubt that there will be explosive growth like the month of June again, but I do not doubt a steady stream of takers lining up until some confidence-shattering catastrophe.