Well I couldn't think of something we could remove from the query language. I just think tag querying is too open-ended, like in theory you could query for a million tags (in practice it won't work).

I like the final point, but I think it makes it bad for implementations. I like the idea that anyone can make a relay implementation very easily, even if they create their own indexes manually. If we start depending on either SQL blackbox magic that would be bad.

Having a query language too flexible would also encourage bad behaviors in application developers, treating relays as full-fledged ultra-flexible databases, which they shouldn't be in my opinion.

I don't know.