Cees, very cool idea.
I'm interested in something a bit more modest - using your p2p network to broadcast Monticello notifications. By "notifications", I just mean that after posting a .mcz file to a repository, the Monticello instance would send out the URL for that file out to all the nodes.
I don't suppose that would test your framework very much, but it seems like it would be very useful, at least to folks using FTP and HTTP repos. And access control would come for free via the magic of delegation... :)