[ocdtrekkie]

Gmail already has a bad hack for this: It reports labels as folders and that duplicate copies of emails are in them.

So the issue is that any other solution would work improperly for Gmail. Client support is a huge part of the problem: If it's outside the standard, clients aren't going to handle it the same way.

JMAP, of course, fixes this.

[jeltz]

IMAP keywords are in the standard.

[ocdtrekkie]

Yes, but how to use them to emulate labels support is not.