Nikon D7100 will kill Panasonic GH3

Very similar weight and size, superior sensor with 1.3x m4/3 crop mode at almost 16 megapixels and faster FPS. Long reach is about the same as m4/3 with the same FL provided that the lenses are of comparable quality.

Lens size/weight advantage of m4/3 isn't always applicable. Nikon 55-300mm DX is about the same size/weight as Panasonic 100-300mm. Same can be said about Nikon 35mm F1.8 vs Pana 25mm F1.4.
Recent video test of D5200 at EOSHD suggests video capabilities of Nikon cameras improved a lot.

OVF, autofocus tracking, better DOF control and significantly better sensor (assuming it's D5200 sensor), all for $100 cheaper than GH3. What's left there for GH3?

Micro 4/3 has its advantages - a combination of compact bodies and lenses. It's a system that can be worn on a belt, a body plus 3 lenses can fit in couple of belt pouches. But it's true only if the body is compact, and that's why I chose m4/3 system. I can pay for compactness, but GH3 is far from being compact. Even GH2 wasn't. These and G5 are just DSLR-sized cameras without advantages of DSLR.

Now, how would justify GH3 being $100 more expensive than D7100 while being inferior in almost any feature that matters?