I don't know much about PKI but it seems to rely on certification authorities (i.e. single source of trust) and there does not seem to be a clear mechanism for

I don't know much about PKI but it seems to rely on certification authorities (i.e. single source of trust) and there does not seem to be a clear mechanism for artists to sign, trade, and 'own' them. But, if you were to create a PKI-enabled digital art marketplace that is able to meet the same decentralized structure and benefits of NFT technology, without the need for a distributed ledger and tokenization, I'm sure many artists and creators would welcome that.