I don't know. If the rumored specs are to be beleived, it does not appear the new desigh will be very conducive to having a bumper. The bumper works well on the iPhone 4 because the front and back are nice and flat and the same size. That way it can wrap around and be stable and at the same time complement the design. I have a hard time seeing how something even remotely close can stay on the rumored design, much less look nice.
I would imagine the Vapor style metal bumpers would be similarly affected, which sucks because there was such a wide variety of cases available for the iPhone 4.
I'm guessing it will be a return to the wrap around cases like the the first three iPhones.