Digital asset tracking of state and ownership. Notarization and attestation services can be used for things like tracking ownership of anything digital. Once digitized and available other applications could be built on top of these primitive functionalities.
Do you need attestation for proof of something? Anything? Health information, Education, Membership of something. This can be the utility provided by NFT’s. Today's top three use cases can be found in digital art, followed by gaming and finally decentralized naming services.