We install multiwire circuits in residential projects all the time. How can you say the running two 10-2's is less costly and less time consuming than running one 12-3? Its just the opposite. The material cost for the two 10-2's would cost about 3 times as much as the one 12-3 and the labor would be at least double. As Bill Addiss just said there is no problem installing GFI's on these circuits once there converted back to two 2-wire circuits. For the kitchen counter receptacles run a 12-3 to the first receptacle then from there run two 12-2's from this box to the other receptacles. Connect the black of one of the 12-2's to the red from the 12-3 and connect the white of this 12-2 to the white of the 12-3 with a pigtail. Install a GFI in this box using the black from the 12-3 and the white pigtail for the line and the white and black from the other 12-2 as the load. A second GFI will then be installed in the first box that the 12-2 connected to the red is run to.
