On draft -09
Suggesting conneg on the service document (or any other resource) is overspecification as this is inherent to the Web. Moreover, this is just a suggestion without any guidance about how it could/should be implemented. Finally, this suggestion is only made for service documents while such mechanism might be used on every other resource as well.
Remove last sentence from section 5.1:
The content of this document can vary based on aspects of the client request, including, but not limited to, authentication credentials.
Absolutely none, except perhaps making some WebArch fans happy.