@mariusor @hongminhee so, what's simplest to me is to keep the structure that was designed 8 years ago.
If you would like to propose an alternative, it's incumbent on you to make the case for it.
I think what you are describing is fine, btw. It is even compatible with the structure Christine developed. If the media upload gets a POST without a JSON-LD part, just store the contents and return an URL that can be used in a later `Create`.
