My partners and I are looking to create a network of multisites and buddypress installs. In short, we need a master admin multisite that will contain within it both individual sites and other multisites with their own administrators.
The domain structure might look something like this:
We want members to be able to have closed network social networking (for a single network within the global network) while engaging with the global network through the same identity. I believe this might mean we're wanting to bind together a similar series of Buddypress installs - one for the network overall, and then an individual one for each multisite in the network, but I concede there may be better ways to solve the networking side of things (there may be regulatory reasons for maintaining silos of information on a specific domain).
The final step is that we are wanting to aggregate tagged blog content up to the primary domain from the entire network.
Hoping someone can shed some light on this!