Will you upgrade from GX7 to a GX8?

I won't.  Some of the features of the GX8 are definitely attractive, such as better EVF and fully articulated screen.  I also really like the idea of having the exposure compensation dial on top of the camera.

But I do use the pop-up flash on my GX7 quite regularly for fill-in flash (especially for outdoor and travel portraiture) and I don't want to carry around a separate flash for this.  I could live with the larger size of the GX8 if it had on-board flash, but I think the size of the GX7 is just perfect.

For me, one of the main reasons for moving away from DSLR (Nikon for over 30 years) was to have a compact system.  I just love that my Olympus and Panasonic lenses use filter sizes ranging from 37 to 52mm vs. my Nikon lenses that started at 52mm and ranged up to 77mm).  The growing size of Panasonic camera bodies concerns me: do they think they need to be almost as big as, or just as big as DLSRs to be taken seriously by advanced amateurs?  And at the same time, deletion of on-board flash (LX-100, GX8)? Wrong direction, in my opinion.

I don't use my camera for video, only for stills, so the 4K video doesn't mean anything to me.

Anyway, I do hope that the GX8 sells well, and that Panasonic continues to develop the GX line, especially since for a while it was not clear if Panasonic would continue the GX line after tepid GX7 sales.  And I hope they put the on-board flash back into the camera on a future GX9!