I think a better point is the N9s are in limited production, while the Lumias are being pushed hard by Nokia and certainly produced in large amounts.

Not to mention the fact that carriers are practically giving them away (Nokia promotions, etc)

"Converting" these Lumias running a useless OS to one running a decent one would provide a cheaper option for people to get a "N9", or make MeeGo-Harmattan more available to the general public should they want to use it without buying a N9 (or perhaps they can't), much like the NITDroid project.

IIRC, some early Lumia 800s have development bootloaders. I might go around and look for these things.

EDIT: It seems that the Lumia 710 is easier to hack, while having the same guts as the 800.