> the adopters would have to keep buying more to keep the price up
That's a logical fallacy. As a Ponzi scheme is not the only way, nor the best way, to add value to the investment. So I don't think that fairly represents the market incentives that exist for the early adopters. Especially given the context of it's creation and the community of early adopters around it.
As I mentioned in my comment above, they are incentivized to have the project produce real tangible value if a) they are interested in seeing the technology succeed and b) they want returns on investment via dividends, which is typically the premise of a longer-term investment.
Even if a percentage of investors don't fit that criteria, I highly doubt they represent the majority. It would only require is a sufficient enough sized majority of well-intentioned investors to keep the project operational.
I'm not convinced the only way it could generate returns - and more generally prevent a drop in value - is by continually adding more investors. I expect they will put in some real effort to make it work as a functioning economic entity.