Is it possible to delegate branches?

Following up denisM's question (http://drupal.org/node/618940), that did not got any reply so far, I come to a much broader question: is it possible at all to perform branch delegation with Drupal?

Let us say I have a corporate web site with a branch for each department. Is it possible to have each departement managing its own branch (this means adding and modifying subbranches) while preventing them from touching the other branches? Or do I have to run a separate Drupal instance for each departement in order to get the job done?