I think that what we will see with the L Mount 'Alliance' is nothing less than an assault on the pro orientated DSLR market dominated by Canon and Nikon. It strikes me that while Canon and Nikon have concentrated on competing with Sony, Leica already and now Panasonic are out to prove that mirrorless high end is the way to go and they are determined to eat into the diminishing high end DSLR market. I think the system as a whole will be big, heavy and expensive with the emphasis on top of the range high quality lenses. I don't see any 'kit' zooms with slow aperture settings appearing. Leica don't do that kind of thing anyway, the Sigma ART lenses don't compromise on size or weight and Panasonic would be ill advised to try and replicate m4/3. I think the point here is to make the whole system as robust as possible to show that mirrorless can handle everything a D5 or 1DX Mk II can. Neither Sony, Nikon or Canon have so far demonstrated any appetite to do that and the Leica SL (Typ 601) is the only attempt to do 'pro' FF Mirrorless so far. I think any resemblance to m4/3 will be only in the fact that the name LUMIX is on the front of the camera.
The marketing men bate their hooks and the photobloggers conveniently bite!
You'll also have notes that the SL is rarely mentioned in comparative reviews of the Nikon and Canon mirrorless offerings. It is always Sony.
Both are FF cameras (the S1 with 24MP and the S1R with 47MP).
Both are based on the L mount which is the same FF mount used by Leica SL cameras.
Both will shoot 4K 60p video.
Both use 2 memory cards – SD and XQD.
Both will have a top screen and a monitor which flips but also can rotate to the side (but is not fully articulated – sadly).
The cameras are larger than the GH5 (but holding the S1R in the hand it feels pretty nice).
There will be 3 initial lenses (at launch) from Panasonic – 24-105mm, 70-200mm (apertures unknown at this point) and a 50mm f/1.4 (Panasonic also promises to have 10 native lenses by 2020 plus quite a few lenses by Leica and possibly some by Sigma).
Both cameras will have in body image stabilization (as well as some lenses that will also come stabilized).