This is all but confirmed. The density will be highest at around the 2/3 back on the foot (just inside the heel. And less dense as you work away from that point, with the exception of the very tip of the toe off, which will be dense as well.
Testers say that it improves the "bounce" factor, and the initial tests are coming back positive. Maybe we'll see a disguised v4's at the trials next week?