The in-body stabilization that works in concert with the OIS optical stabilization looks promising, this will appeal to low-light and hand-held video shooters as a companion body to their GH4s.
Many are upset with the larger body, but I am happy to see a larger body with more individual knobs, and fewer tiny menu buttons. I agree that it will probably become a popular body, will consider one myself once any bugs are worked out.
In the production bodies, I hope they decide to switch back to a 3.5 mic jack, like other Panny bodies.