I wouldn’t want ALLUPPERCASE identifiers on my URLs for instance. I presume that would be one of the most common scenarios it would be used in.

Well, it will still work but you'll lose the benefit of it.

Most of these don't look like SHOUTING to me. They look uppercase but not aggressive.

You don't want upper-case in URLs for social reasons. It simply looks out of place, takes more screen real-estate, and stands out unnecessarily.

I'm just saying, if canonical is good enough, "S/5" fix isn't sufficient to get a whole new standard then. If it isn't good enough, then the value this one promises over Crockford is arguable due to lack of I/l/1 aliasing.

I downcase all ids, sometimes this includes uuids and string ids.

This is suggesting that you don't.

It shouldn't be that hard to start using it in the canonical form - just start treating IDs as if they're case sensitive.