I really prefer m4/3 for size and mobility and I'm reasonably happy with my GX8s. The m4/3 cameras and sensors are falling behind, though, considering the tech that's showing up in these recent releases. I've got a lot of Nikon glass (and a D3 and D800) but I've not updated my Nikon system since the D800 because I've been focusing on m4/3, but if Panny and Oly don't move forward with their compact cameras, I may move to the Z cameras. (I recently spent some time shooting drag races, and took the D800 because the races went into the night, and the Nikon's low-light response is better.) I'm waiting, though, for rumors about a second generation of Zs and for a wider spread of native lenses for the new mount. For now, I'm good.
About the new FF Panasonic...Somebody in a different thread emphasized the tie-up with Leica, which has caused me to re-think that a bit. Nobody except a few fanboys (IMHO--don't assassinate me) really thought the Leica digital cameras were that great, and they were forbiddingly expensive. It's the Leica *glass* that everybody was hot for. A really excellent (and cheaper!) camera/sensor with Leica glass could be a compelling system.