The pins wouldn't be patented. There are 20 of them in a row, the top 3 and bottom 3 being used for power, leaving 14 pins in the center for everything else. The challenge would be all the chips/electronics you don't see, embedded in the dock, that manage those 14 pins. There is also more than likely a chip in the standard power supply to manage the 6 pins.
Zog1971, it's a great idea and one that never occurred to me. So kudos to you for thinking of it. If the connector looked just like the power cord, then the industrial design possibilities would be endless. The "dock" could be flat and the same dimensions as the SP3, allowing it to be easily transported with the SP3 to meetings. This would allow for expansion slots for things like a GPU, hard drive and a hot-swap battery.
That would a killer add-on for sales teams that have to do demos at prospect/customer locations (like I used to do). The whole thing would fit in a backpack and one could work on the finishing touches in the car passenger seat or on the plane/bus/train.
I like it. MS you listening?