The DID specification is being developed by the W3C Credentials Community Group. If you are interested in DIDs, we welcome your participation. Information: https://w3c-ccg.github.io/
DID spec: https://w3c-ccg.github.io/did-spec/
Exactly. If the recipient is providing the address then they can (and generally should) choose different addresses. If for some reason they wanted a specific grouping by address, that is their choice. Although, as you point out, it should never be necessary as long as the recipient can easily manage these certificates (for example, through a wallet).