That mockup looks like it has serious potential if they could actually make the production model in the same form factor. With a 20 (40mm) pancake lens on that thing, it would be a very versatile carry-around camera that gives DSLR quality photos but doesn't automatically make you look like a tourist.
I must say that it would look quite awkward with some of the higher grade 4/3 system telephoto lenses out there...actually, even the 14-140mm that was announced with the Panasonic G1 looks like it could dwarf the rest of this camera.