This looks good to me. Any objections @json-api/owners?

One question is whether we should say a 404 MAY be returned or SHOULD be returned. I'm tempted to say SHOULD, because HTTP's most recent specification pretty clearly implies that DELETE being idempotent doesn't mean you have to return the same status code each time (which was the argument for MAY in #1023):

Idempotent methods are distinguished because the request can be repeated automatically if a communication failure occurs before the client is able to read the server's response... It knows that repeating the request will have the same intended effect, even if the original request succeeded, though the response might differ. (Emphasis added.)

But, if there's disagreement on a SHOULD, I don't think that technical debate should hold this up, as we can always strengthen a MAY to a SHOULD later.

Even though I am not part of the owners, I would be in favour of SHOULD.

I am fine strengthening to a SHOULD here as well. I think a MAY is almost meaningless compared with the general catchall response section.

@lukasoppermann please update to SHOULD and then we'll get this merged.

@dgeb updated.

Thanks @lukasoppermann!