Ed, thanks for posting this question.  Each user has their own master categories.  If you have shared your contacts with someone else, adding/changing/removing master categories or selecting which category a contact follows under introduces a lot of complexity.  Whose master category list would you be affecting?  Or which master category would you show?  So in essence this was a deliberate decision to exclude from shared contacts.

 

However, how would you like to see this implemented if we did include it?  Would you see the master category of the shared user?  Obviously, privacy issues could arise if their categories were visible.  What are your insights and feelings?