I think this is tricky.
You know buddypress. Buddypress brings a bunch of functionalities and features, focusing people. A new user can register for a blog and this will be hosted with the domain http://newuserblog.sitename.com.
My vision – In a WordPress multisite a new user can register a subsite (not a buddypress blog, without the buddypress plugin) with pre-defined custom post types/taxonomies, its own database tables and its own subdomain (like a country or a city).
The domain should look like http://newsubsite.sitename.com
(With this new subsite registration plugins and themes should be activated depending on the membership/package. So I call it a "buddypress for non-peoples with wordpress structure")
Has anyone a idea for a existing plugin? Or do I have to develop one by myself?
Thanks for a hint.