It sure doesn't look that big to me. After all, it has OSS and must cover a FF sensor. Anyway, who says that the camera must always be small. My hands are not comfortable with small cameras and I'm primarily interested in getting rid of the mirror and mechanical first shutter. I've got the grip ordered and plan on keeping it mounted full time. I would be using this as a second camera when shooting sports. Of course, I'm thinking more of a fast autofocus E-Mount FF coming on, or before Photokina. My immediate need is related to shooting sports video. So, the tracking abilities are somewhat important. This use requires that the camera be mounted on a tripod with external microphone and monitor.
I suspect that you will need to go to a smaller sensor and dump the O.S.S. in order to design a small high quality lens with the same effective zoom range.