Extending the above:

I am not sure how much the total users of smart phones have their own cloud. I would guess, not too much.

So having a cloud service replacing their proprietary one, would be a good start for people who do not have the knowledge so far to run their own servers.

Also having such thing, would allow you to have such servers locally, and use it transfer files e.g. between your devices without internet.

The cool thing about having a layer like this, with the nostr level abstraction, is that it is easy to switch, and gives superpowers to apps with interop.