Could you tell us more about what you're trying to do exactly? Once you start outputting, headers and content are usually known (even if content is being streamed you know the source).

We cannot make the method static as it would be a BC break.

In my case i avoided the issue in the end. Since my initial attempt was wrong, unrelated to this.

And since this is a BC break, you can close the issue. Convenience is less important and since there is no active use case anymore there is no need for this.

I did make a factory that was creating response objects for me but needed to have some headers defined/determined before the response object was actually created.

A refactor had me remove all that logic, which to be honest was kind of nasty anyway.