If there's a way where we could say "this specific key will be this specific value in order to mean this specific scenario", I'd support that! But. Then. Isn't that the status that's I'm talking about?
I never said the error message can't or shouldn't be introspected and totally agree we should send our clients as much info as we can to make it clear on what they can do to fix any errors!
I just really really like being able to say "this specific field tells you, across all apis, what happened with this request" and don't see the gain in pushing that data into good luck finding out what key.