Not if the only registered media-type is 'application/hal+json'. We should 406 and give a list of accepted types in a service. So, our serializers should not be some dynamic thing that mixes and matches. It should be explicitly opinionated on media-types. A particular mime-type like 'html' can (as we supported in Crichton) respond to different media-types in a ranked fashion. This is more what we should be doing I think. Am I missing something?