Interesting thought process and experiment. Perhaps a significant flaw at the end assuming that all drug buys are in BTC. With trillions of USD $100's floating around the world, will be a lot of drug buys with that currency into the future.
If you assume even 50% of drug buys remain in fiat, then floor under BTC is cut in half.
Would be interested in your thought process on setting a "value" on BTC using some method comparable to how the "value" of gold is determined.
May produce another interesting number as a thought experiment