As for "Crypto-less federated systems like Mastodon and friends" - you have to ask yourself why they don't work at scale. That's the key insight of Bitcoin. You need to have a system-native incentive for the nodes to do their thing, and this system-native thing (BTC the currency, in Bitcoin's case), should have outside value. Many wiser people have said this (not on HackerNews maybe), that money is the only use case for a blockchain.