Brander and Joel started building Subconscious, a local-first decentralized note-taking app. They began with the protocol that would power the app - Noosphere. Noosphere is permissionless and open source, like HTTP or IMAP; anyone can build on top of it
If this is a 'return to the web' as stated then why a new protocol? The web already has its protocols. Creating your own for your app and saying well if the app goes the protocol is still there for you to build your own is exactly what silo's like Evernote also did (there's always our own xml-based export format, you're not locked in, and they actually are not wrong).