I think that GP's point was that a standard a la HTML or RSS should exist and be embraced by the OS. Something like Syncthing, I guess (just naming one of the first hits I got from searching, I haven't really kept up with what is being tried in this space).

https://en.wikipedia.org/wiki/Syncthing

Don't be so sure -- IPFS provides a possible path. We will see if it works.

Someone, somewhere has to pay for the disk.

Yes IPFS the collective internet prices and earns for contributing disk.

It's the protocol that's non-proprietary, not the service. IP is non-proprietary but you still have to pay for servers.

Why would non-proprietary preclude paying for storage?

Because each of those is trying to profit from it, not just pay for the storage. Thus, branding, and thus, they make them private and proprietary. Is it right? No.