> What happened instead was that the technology turned out to be one of the worst threats to global warming since farting cows (yes,yes, i know, ethereum makes it all better)
This has been overstated by critics. It's currently at something like a half a percent of world electricity usage. Which as an absolute number is really big, but as a contribution to global warming it's just not a meaningful percentage. And even ignoring something like proof of stake or Chia, it gets solved the same way as the rest of the problem -- replace generation capacity with non-carbon sources. Institute a carbon tax. Then people will mine Bitcoin using renewables and that'll be the end of it.
> the intermediary- and fee-free part never actually worked out at all (because people need accounts somewhere, sorry, wallets)
It turns out people often want this because they don't want to lose all their money if they accidentally drop their phone in a river.
The key is to make sure that it's still possible to do it without an intermediary, because that's what keeps the intermediary from becoming an abusive chokepoint for authoritarian policies, since any attempt to implement them there would only overtake the benefit of their convenience and cause people to switch to direct transactions.
> bitcoin and others turned into a speculating collectors' frenzy that while technically, perhaps, not as absurd as beanie babies or dutch bulbs, is generally adjacent to such historical fancies.
This was made significantly worse by the design of Bitcoin in particular since there is a limit to the amount of Bitcoin that will ever exist. Which makes it not only not inflationary but heavily deflationary, which promotes speculation.
It's plausible that some other cryptocurrency that limits volume only in proportion to some scarcity (whether or not it's still compute) but has no fixed maximum number of coins would be less subject to speculation and therefore less volatile. And then the lower volatility might cause it to have higher adoption in the long term.