Actually this rebasing is almost 'porting debian to N900' (using maemo kernel). When this is done, it makes Maemo5 more worth for porting to another devices. It makes porting just slight easier. E.g. there are some bsd-style-licensed packages which Nokia closed (libjpeg62), and some open source packages, which Nokia bought commercial license and closed. They are free in Debian.

Check roadmap for make maemo5 portable to another devices: http://wiki.maemo.org/Fremantle_closed_packages