To be honest I can't see the point in this from a development perspective. To port and test an entire operating system onto new hardware would take a huge effort. The effort would be better spent porting the actualy applications to the new OS and running them at full speed.

As applications are being ported from one release of the same OS to another there is a well known migration route for most things. GTK+ used in OS2008 is available in Maemo 5 so the majority of differences are actually UI requirements and redesign.