I see the UMPC as one of those leather jackets you might have seen cameramen wear but less bulky. Pouches everywhere with wires going from one to the other where you have many connected batteries and CPUs. You'd have a screen on the arm or display goggles, and a bluetooth "gravity joystick" (that's my invention based on ordinary mouse technology where a ball rolls freely on contacts when you tilt the stick ) in the other hand. Everything could be light and made with today's technology...
No one is courageous enough to market one, because it's not a toy.