BuddyPress.org

Since you are talking specifically about altering how WPMU deals with blogs, I’d suggest posting this question on the WPMU forums so that their gurus can answer. Whereas you might receive an answer on the BuddyPress forums, the WPMU forums is the more appropriate place for such questions.

I advise that you first do a through search of the Mu forums before posting.

https://mu.wordpress.org/forums/