Have you tried speaking to the Mer team to see what adaptations are required to make Mer work on this device? If you can get the drivers and any other h/w adaptations specific to the SGS II to work with Mer, well we might be looking at a new direction for all of us! The only thing is they (the Mer team) seem quite aligned with the whole RMP setup, so if you want it more Debian-ish then you'd probably have to take it apart a bit.

As to porting Maemo5 itself, why? There is a lot out of date and a lot very hardware bound. It's good for what it was designed for - the N900, but very much all or nothing (both device & OS or neither).