Gateway NoFetch Enhancement

Currently, the "NoFetch" config setting on gateways only helps if the gateway is the node also in charge of storing content.

Instead of trying to tackle gateway abuse by blacklisting hashes, are there any tweaks that could be made to go-ipfs / libp2p to have there be a "NoFetch except from these specific peers" sort of enhancement?

People likely relevant to this conversation: @Stebalien @raulk @mburns (feel free to tag any others)

Potential relevant github issues:
* https://github.com/ipfs/go-ipfs/issues/6565 (whitelist peers for the content to come from)
* https://github.com/ipfs/go-ipfs/issues/6097 (potential fetch whitelist from "groups" that Juan mentioned in this thread)