https://www.cnet.com/news/rumored-panasonic-full-frame-mirrorless-reveal-on-sept-25-is-odd-but-plausible/

There's also a countdown page for its press conference, which means something big is probably in the works.

The news was broken by 43rumors, which gives it an "FT5" probability rating -- its highest level. And it comes after similarly high-probability rumors in July (which I missed) of a high-end Olympus model with a new sensor format. Since Olympus is also a Four Thirds company, it's pretty compelling evidence for a new-size sensor.