Specs, much less actual images, are scarce... The few available pieces of info suggest a rather odd camera. Every site that's seen the mockup mentions that it's big and heavy, and state that it's larger and heavier than a GH5... By how much? The Leica SL is mirrorless (and not medium format), but it's the size and weight of a D850. Is the S1/S1r in that class, or is it somewhere in between the larger of the ordinary-sized mirrorless cameras (the GH5 is the largest of a class that includes the A9, A7rIII, Z6/Z7, EOS-R, X-H1 and E-M1 mk II) and the D850/Leica SL class?
It seems to have no phase-detect AF - an odd choice in a world where phase-detect performance on mirrorless cameras is increasing so rapidly. As to be expected from a Panasonic, video features look excellent - 4kP60, although with no mention of data rate (and the SD slot hanging around concerns me on that account - only the very highest-end SD cards can keep up with the GH5, and any hope for a much higher data rate seems to be quashed by the SD slot unless there are some video modes that are XQD only).
The two most important questions are going to be the quality of the sensor, and of the lenses. Is the (Samsung? Panasonic?) sensor going to be comparable in quality to the Sony sensors in the same pixel-count range? The EOS 5Ds (the only camera we've seen with a very high resolution non-Sony sensor) was a disappointment in this regard. While its resolution is superb, its dynamic range and noise capabilities are quite a bit lower than the Sony-sensor alternatives, including the older generation of 36 MP sensors as well as the newest 42-46 MP generation. Will the new sensor be similar to the Sonys? More like the Canon 50 MP sensor? Possibly even better than the current Sony sensors (unlikely - I would expect that anything that significantly outperforms the A7rIII sensor and the D850/Z7 sensor would require a 16-bit ADC, and there's no sign of one here)?
I haven't seen anything about the Leica SL lenses that justifies their size, weight or cost. While Sigma Art lenses are nearly always big and heavy, you get a lot of performance for the weight...Will the new Panasonic-branded lenses be a more compact option while maintaining quality? Another line of reasonably priced, but heavy lenses to go with the Sigmas (which I'm assuming will show up on L-mount pretty quickly)? More expensive lenses like the Leicas? A line of cheap consumer zooms? I hope for the first option...