Proof of Stake will keep actual resource costs maintainable, and Blockchain does do some cool stuff for decentralization, and therefore federation. Right now Lemmy instances are tied to DNS. Hopefully in the future they will be tied to cryptographic assets. Distributed Autonomous Organizations are a great example of the potential.
Blockchain is well suited for storing authentication and provenance information. The Fediverse could benefit from blockchain stored instance, user, and community metadata.