What do you think people will make the Query request body? Most everything will use this for JSON but it could be anything so what other interesting things do you think will go in there? Query 1 + 1 and get 2?
I'm curious too. Unless the developer is really passionate about this I don't think a dev will risk (potential) compatibility issues or unexpected footguns to use this when the workarounds do seem to work quite well already. I just dont see the benefit but maybe it's because I am just not aware of a real world use case; happy to be corrected.
So opensearch also allows you to POST search requests, but those are uncacheable
QUERY would fit here perfectly - it's probably trivial for opensearch to add but it will take some time for clients to catch up.