May be interesting to compare to smartphone adoption s-curve and the total population. Slope is likely to be similar from a technology adoption perspective. If you assume all fiat replaced then not sure 1M is enough.
In my application of the model, the population consists of all speculators who will ever buy bitcoins.
Problem is that speculators sell, and
adopters of washing machines didn't (c.f. the linked chart of technology adoptions over the past 100 years).
Wrong model.
You are right insofar that speculators sell.
To clarify, my model assumes that bitcoin prices climb higher over time to a guessed-at maximum price due to increasing numbers of speculators. The logistic model is justified because eventually the number of new speculators taper off, e.g. limited by the global adult population. The motivation and behavior of these speculators affects price action - but I am abstracting these properties by simply counting speculators as the modeled population. When I guess at a certain maximum bitcoin price for the model, that translates to a certain degree of speculator commitment and resources.