From a security point of view, you need to physically segregate US arriving pax from pax arriving other countries. Just letting pax with US boarding passes and identification skip security won't work if US arriving pax can mingle with pax from other countries before security. Given that I suspect that this will be implemented by allowing pax with an ongoing boarding passes to exit directly into the departure area on the 3rd floor after exiting the jet bridge rather than being required to take the escalators/stairs up to secure arrivals areas on the 4th floor. Additionally there will be security to prevent pax from going back down, once they have gone up to the 4th floor unless they go back through security.