yep that would fix it. just needs a little docs change.

a "quick start" really should just work when you copy paste them.

Can it be some other content type?

why does an API that only accepts json need me to specify in a header that it’s json.

just assume it’s json. you’re gonna parse and validate it anyway.

If it turns out that someone is willing to pay for some other protocol then they just have to hook it up to that MIME type and start serving. It might be possible that they can derive an implementation of that protocol from their data schemas.

If they hardcode JSON such a change would be breaking for their previous users.

Why would it be a breaking change? Just continue assuming JSON if no Content-Type is provided.

that's actually a reasonable point.