I am a long term bull, and I tend to agree with the trend line premise. However, I have a problem with this analysis. When does it change? I mean you could extrapolate this to mean Bitcoin will be worth 100MM dollars on a long enough timeline. I think we all agree that Bitcoin will not be 100MM a piece, so the question is, at what point is the trendline no longer relevant? When do we need to remodel the trendline?
The difference between exponent and S-curve becomes noticeable only after it reaches about 1/2 of maximum (until then all differences can be explained away as volatility). At the current line (10x a year) 1/2 is less than 4 month. So if the eventual bitcoin price is 1M, we will notice the signs of saturation only 3-4 months before the trendline will cross 1M mark.
If 3-4 months is too short a notice, we should look for an input outside of price data. We have to figure out what will be replaced by bitcoin and what is the current cap of this would-be-replaced thing. Gold? Internet money? Black market? Gray-market? African money? Thirld-world money? US Dollar? MB? M1? M2? Bonds? CDs? Hedge funds? Pension funds? There were a number of threads with such discussions a year ago. Nowadays, with one-year-long bear market, such topics aren't so popular. Instead people are discussing how
low will bitcoin go.
EDIT: added some articles ("a"s and "the"s)