No way will it be that thin.
If it was, how would Apple be able to top it? It looks nearly 40% thinner than the current model, and that's just way too much!
Having the phone be 10-20% thinner will be perfect for the 6th model (since I believe the 5th model will have the same body).
10-20% thinner, will be already thinner than any phone out there.
Hell the iPhone 4 is thinner than these new phones coming out (HTC Thunderbolt, Motorola Bionic, etc).
It's also too short. You can keep the phone the same size (height), and still be able to have a large screen. Maybe make it a little wider, like right in between what you have, but that's just me.
Can you mock up a design with the suggestions I made? 20% thinner than the current iPhone 4, same height, width in between your concept and the current iPhone, and a screen size between 4-4.3 inches (do I dare say 4.5 inches?).