It could be interesting to have a search engine that only shows results that have human attestation via digital passports. Of course I'd prefer that to work without necessarily revealing the identity of the poster, similarly to how anonymous "sign-up tokens" for accounts would work, to prevent sybil attacks.
Marginalia doesn't actually use whitelists though, but it does give preference to results from known human websites, as well as sites that are linking to and being linked from that set.
