It would not need a people mover. The idea of midfield customs is that you can go I-->D while staying in concourse C/D, and you don't have to take the people mover back to the international arrivals building and then get on the aerotrain back to C/D for your connecting flight. So the current system, and presumably the new version in any new C/D, would achieve the same thing without the need for people movers (this doesn't address anyone arriving on non UA flights who are connecting, but that's probably mostly limited to *A pax arriving in terminal B, who then need to get to C/D for a UA connection).