Will coordinates actually add substantial value? If the answer is yes than x and y percentages sound like a good idea. Everyone should be able to easily adapt that to their UIs.

Do we really need this? I don‘t like being tagged. Shouldn‘t rather extend the profile (maybe NIP-05 even) with a face feature vector for people who want to be taggable? Clients can then make their own thing based on this.

It would be great if the tagged people can ack the tag before the client UI renders their npub. Or opt out from a specific tag.