I would find it very useful to be able to assign attributes to groups instead of just Users or Everyone.
Repositories often contain different sets of documents for different groups of users. Even if you have just a departmental repository, you may have cases where groups in that department access their own documents oblivious to other groups who access their own docs.
My initial use-case had to do with template fields in column headings, but I'm sure there are other settings which would apply to one set of users in a repository and not others.
Of course, there would be questions about which attributes apply when there are conflicting attributes. I would assume that the attribute with the smallest scope would apply. "Everyone" attributes would be superseded by group attributes which would be superseded by user attributes.
Assigning attributes is very useful - it helps with the user experience and with consistancy - especially coming from Version 7. Adding the ability to assign to groups would increase that usefulness.