Both cameras are based on the L mount which is the same FF mount used by Leica SL cameras.
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 significantly larger than the GH5
There will be 3 initial lenses (at launch) from Panasonic – 24-105mm, 70-200mm (probably with a constant f/4.0 aperture) 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).
Image quality, build quality, operability, and performance without compromise
New processing engine
Fast and very accurate autofocus (combination of high-speed contrast detection autofocus and DFD technology)
The AF also includes deep learning Ai
High-precision, high-speed shutter
RAW output video rumored (big question mark here)
Very high-resolution viewfinder - the highest-precision finder in the industry