I have come across systems that use GET but with a payload like POST.

This allows the GET to bypass the 4k URL limit.

It's not a common pattern, and QUERY is a nice way to differentiate it (and, I suspect will be more compatible with Middleware).

I have a suspicion that quite a few servers support this pattern (as does my own) but not many programmers are aware of it, so it's very infrequently used.

Sending a GET request with a body is just asking for all sorts of weird caching and processing issues.