Andrew, the problem with a much larger sensor than the tiny video chips of yore is that you have to use a significant zoom lens on the camera (or a long FL prime) to couple to the scope eyepiece/TC train. I've tried my GH4 w/ the compact Panny 14-140, but just too bulky, with a relatively small circular image shown, or no focus-able image all. My next iteration was the Sony HC1 FHD camcorder, but never found suitable astronomic "seeing" to warrant the time and effort of setup with the 9.25" f/10 scope.
What I have done with it is total solar eclipse recording of solar flares and detached prominences, but with a very compact and excellent 4" 1000mm f/10 reflex scope w/ tube length only 8" using an eyepiece coupled to the Sony lens, but no TC. First pic below with the VGA res. TRV-900 of the striking detached prominence - Africa '01; the second with the FHD Sony of the "hedgerow prominences" I've not seen imaged in this detail - Turkey '06. For the recent eclipse I viewed and imaged from Madras, Oregon, I used my GH5, Canon 100-400-II w/ 2X TC shooting 4K in ETC crop mode (2.7X crop factor), plus 2X dig zoom or this to 1080p res and 5.4X factor = 4320mm EFL. Tech. screwups on my part nixed any views of the pretty unimpressive flares at this mag.