The French website Mizuwari talked to Panasonic France managerin Mathilde Lécuyer. She shared quite some interesting tidbits:
1) Panasonic’s first goal is to give current MFT users a possibility to step up into Full Frame.
2) There are some physical limitations with MFT that Panasonic wants to overcome with Full Frame. Panasonic had no doubt that theyr would arrive in full format one day or another, because technically speaking the 8K on Micro 4/3 is complicated, if not impossible.
3) Panasonic will keep the promise and announce an 8K Full Frame camera by 2020 (L-rumors note: Of course this is going to be L-mount)
4) The full format will not meet the expectations and needs of a lot of users who will choose to turn to Lumix, if only because of size and price. So, of course, again, we will continue to release Micro 4/3 lenses and cameras, and our 10-25mm f / 1.7 under development is a good example of this.
5) Already 8 years ago Panasonic was thinking about going Full Frame
In short: MFT sensor size isn’t enough to make 8K cameras and therefore they had to step up to Full Frame.