Wow, this is really brilliant, and there's the potential for high disruption. Only for file sharing? Not as I see it. I'll have to make time to try this out asap.
And, not that it's the main idea, but merging the file paths and an email address is something 'everyone' can understand. Twitter built a whole business around @somebody.
edit: Many potantial uses are described in the overview. Read the whole thing. https://upspin.io/doc/overview.md