I don't forsee an f-150 ever being able to safely tow 10K LBS. It simply doesn't weigh enough and doesn't have the driveline or suspension for it. However, I have heard a similar story from Ford - it was from one of their product managers at the car/truck show a couple years ago that was here in Houston when I was drueling over the Super Chief.
Ford F-250 Super Chief Tri-Flex Fuel Pickup Truck
The story I heard was the engine would be strong enough for the larger trucks.
I also liked this one:
2000 GMC Suburban with VW 1.9l DI diesel - TDIClub Forums A VW TDI engine powering four electric motors in a GM Suburban was the winner (if I recall correctly), looks like the original site is no longer around.