Origami is a mobile XP platform. WinMo5 doesn't have such a grand application base. The hardware alone on the 770 should hold WinMo5 but would require a wholly different firmware base. However Microsoft requires the actual hardware developers take on initiative to make it Windows Mobile compliant. Will Nokia do that? Will the application base for Windows Mobile 5 support the 770's resolution? Nope.

Simple answer:
Theoretically possible.
Practically impossible.
Not enough market to support the cost of Windows licenses and development.