It's a bit more difficult than usual. Most of the Nokia 'lending of hands' was to subcontractors who developed open source components which then find their way upstream, to other developers, etc. Unity on the other hand is fully ocmmercial and does everything in-house, they have stated several times either they do the porting, or there is no porting. So basically Nokia would be just footing the bill for Unity to have another platform (and to draw income from). It's a bit of a catch 22, but really, it's much more up to Unity to make that leap of faith than Nokia.