P2p is generally bad for this usecase. P2P generally only works for keeping popular content around (content gets dropped when the last peer that cares disconnects). If the content was popular it wouldnt need to be archived in the first place.

I think if you take this idea far enough you end up reinventing taxes from first principles.

Imagine a proof-of-space cryptocurrency that encouraged archiving long-tail data.

/dev/random as a free money printer? Sign me up.

IMO there is actually a very low hanging fruit here, even without P2P or DHTs we could have an URI scheme that consists of a domain and document hash. It is then up to the user to add alternate mirrors for domains. Aside from privacy, it doesn't really matter who answers these requests since the documents are self-signing.