Isn't the signature itself basically an NFT? Or can we get super meta with bitcoin signature NFTs on the bitcoin chain?
Actually yes, the signature itself is basically an NFT, anything unique is actually an NFT.
The initial idea was to convert the old Bitcoin addresses into NFT, but the problem is that Private Key is owned by the old owner and the new owner, so to solve this problem (OP) developed the idea to make an NFT from the signature chain.