Proponents of cryptocurrencies could easily fix this by creating one that grows by k% forever (like Friedman's k-percent rule). But they won't because this destroys the "get rich quick" aspect of the technology which they won't admit is the main thing they are drawn to.
If they were serious they would have fixed this problem and made sure bitcoins generate long run inflation.
Could bitcoin's popularity stand on its own with just its net benefits as a transaction medium after the allure of ponzi investment has been removed?
Plus, Bitcoin isn't deflationary by any standard definition of the word. It's not inherently price deflationary of course, since that's dictated by demand. And the money supply inflates, albeit at a known predictable rate which slowly decreases over time.
This supports the hypothesis that cryptocurrencies are not useful as currencies and people mostly like them for their ponzi investment allure. This would make them not viable in the long run, the digital equivalent of gold but with even less intrinsic fallback value.
The latter I'd say are better served by a currency that encodes a price stability algorithm rather than a hyperdeflationary one. The former on the other hand...
Bitcoin or Altcoins are not a get rich quick scheme. They provide value for users by making transfer of wealth globally possible. The traditional infrastructure cost for this is many trillions of dollars (you pay it with taxes and inflation).
Otherwise, it basically blocks net aggregate marginal investment. It transforms people's savings from being tied to real physical things that are going to create value in the future when they want to redeem those savings to an accumulation of idle bits that won't be able to produce anything.
This is also the reason too low inflation in the eurozone for example, is so destructive.
Bitcoin is volatile, but its extremely useful as money (if you live in Argentina or Zimbabwe, etc.). Descendants types will be far superior to government debt as money. Deflation basically means price-appreciation versus other assets. Inflation as its currently happening is fraudulent accounting on a unprecedented scale. The blockchain by contrast offers honest computer based accounting.
Because they were late in their money printing, velocity dropped and they had to print much more getting much less effect per unit and yes did put the world at risk of future spike of inflation if this money starts moving.
Sufficient high, well controlled, early enough inflation prevents velocity from dropping, prevents the investment and labor markets from jamming, prevents from having to print too much, prevents large stockpiles of idle money from accumulating and prevents later difficult to control spikes in inflation.
You mean, it could be useful as money in theory, but in practice it is not. It is not practical to meet one's needs transacting in bitcoin even in affluent regions where computers, internet access and general computer literacy are ubiquitous, so those economically strained regions where citizens are struggling just to meet their basics needs are places where bitcoin is a complete non-starter; it is not at all viable.
There is no evidence whatsoever that "too low inflation in the eurozone is so destructive". You're mistaking dogma with fact.