I think the goal of Moebian project is clearly stated on its homepage: https://garage.maemo.org/projects/moebian/

The purpose of this project is to integrate all Maemo5 (incl. proprietary) and future MeeGo components into a Debian base system running on the Nokia N900 and future devices, for the native installation of Maemo5, MeeGo and standard Debian software.


Picking your words: "want to install a normal debian (using the available debian armel) and port missing parts and modifications to it, maybe rebuilding armel packages with optimizaition for the omap".