I recently submitted the “Untransferability Indicator” EIP. Currently it is for EIP-1155 tokens, but eventually I want to implement untransferability for any token specification.
I support your idea if it can be applied to ERC-20 token.
IMO, any tokens have transferability by default. Untransferable tokens is the specific case of them. So, I think it’s better “Untransferability Indicator” or “Untransferability Interface” than “Transferable Interface”