That can be done out of band, doesn’t need to be on the spec; much like negentropy is useful but doesn’t need to be done via nostr nor speced within nostr.

nostr:npub1ye5ptcxfyyxl5vjvdjar2ua3f0hynkjzpx552mu5snj3qmx5pzjscpknpr talked about doing something similar to NIP-65 for blossom as well as the idea of creating a DVM market for “I want to find file with hash x and willing to pay y sats” which are two very useful building blocks of this system