When I transitioned from Gmail to FastMail, I had to get used to using folders again instead of labels. While it was painful, I am glad I am no longer using labels, and I have no intention to start using them again. I vastly prefer being able to rely on the basic email client functionality in any given mail app, and using goofy nonstandard parts like snooze and labels makes that difficult.
I appreciate that with JMAP, FastMail has essentially become the first entity to do labels correctly, with a freaking standard behind it, but client support isn't going to be there for many years so I will avoid it. The big upside for me is it'll take away one reason people say they can't leave Gmail.
Is there any reason for why IMAP keywords cannot be used for labels by e.g. having some prefix for the keyword which indicates that it should be interpreted as a label? Client support is of course needed but to me it seems like the IMAP protocol already supports labels. Maybe IMAP lacks the ability to enumerate all labels?
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.
I appreciate that with JMAP, FastMail has essentially become the first entity to do labels correctly, with a freaking standard behind it, but client support isn't going to be there for many years so I will avoid it. The big upside for me is it'll take away one reason people say they can't leave Gmail.