Feature detection and Accept: application/signed-exchanges headers

[kinu]

For feature detection some of us have been discussing that we could add Accept: application/signed-exchanges headers. However given that SXG can have any resources it looks the UAs that support SXG always need to attach / append SXG type even when anything can be accepted, so it could look something like Accept: application/signed-exchange;q=0.9,*/*;q=0.8 for default, non-specific subresource requests. Would it be just or if we want to think about alternative feature detection mechanism (e.g. specific headers etc)?