It needs a lot of processing power to do so and it looks like GX8 doesn't have enough.Hmm. Interesting but it's not using the floating sensor it does in stills mode - it's just an electronic stabilisation applied to the image surface. Which is very different and I suspect not great for image quality (and perhaps not much better than applying stabilisation in post). As IR say, the GH4 is still the video flagship by a margin.
On the same note, the on-sensor stabilization is the same technology as pixel shifting for higher res. It is offered on some high end cams like Hasselblad and a far more affordable Olympus EM5 MK II. Both have Sony sensors, as does GX8. So, why doesn't GX8 offer a pixel shifting option for an improved res? I would think one has to thank Sony for that.
But this does leave GH5 with something to look forward to. Let's say a 22 MPX sensor has that pixel shifting technology that can deliver a ~ 60 MPX quality image in real time (Olympus says they will be able to do it on their next generation cameras) and that will make it a far more capable stills product to go along with all the video.