Mmm, Lots of questions...
One of the draws to Ubuntu, is the ease of use. However, Hildon is possibly an even easier UI to use, especially with fingers.
If it can run Ubuntu 12.xx, why not Debian 7-arm? From there, I wonder - how portable are the Hildon packages? And, can the devices's native software, like phone, sms, etc. be meshed along side Debian/Hildon/Maemo/whatever, so both can run simultaneously and neither conflicts with the other?
... Is this the naissance of Maemo 7(?) - one that runs on non-nokia devices? If so, might all be quite "disruptive"?