Frankly, I don't see much use in blockchains besides public verifiable high-importance transactions where a significant number of parties does not trust each other, and some may be actively subversive. That is, a public ledger.

For less public cases, mere encryption could suffice, which is much faster. Most communications are between only two parties; they can check each other's key fingerprint via phone or a third party they both trust, if they even bother.