BuddyPress.org

How about something for the site admin. A few ideas. A blog clone plugin. Setup one or more clone blogs including plugin settings, then depending on the role, group or whatever of the new user it would clone the blog with all the setting, menu, etc. already setup. This would of course go great with a true role-manager for wpmu that could create site-wide roles, or edit the site-wide rights of any of the roles. Which used with a wpmu specific adminimize plugin that would recognize not just the old roles, but newly created ones too and then set the menus site-wide for each of the roles (or if we can clone blogs, at least would recognize newly created roles). This would be great for educational or setups that want to charge for extras (although I guess these are kind of wpmu ideas, but still very relevant to buddypress too.

Another tack would be to create some educational plugins for quizzes somewhat like Moodle without Moodles rigid structure. (But those are more WordPress specific rather than buddypress) although buddypress with individual eduacational spaces for each student, but sitewide feeds of grades to teachers would be great. And schools need the free stuff with money hard to come by from administration types who think computers are just big calculators for adding up costs.

And yes, I definitely agree about the privacy issue.

Lots of great ideas above all the best in making your choice and best of luck at GSoC.