Any digital data can be converted to an NFT so physical coins, stamps, furniture and antiques cannot be converted to NFT. But you can convert a song to an NFT but who is going to buy a song which should not be heard by anyone else?
Some collector or real connoisseur. The question is not even who will buy, but who will sell. They will buy anything from a famous person, because in the future it will be possible to sell it more expensive