If I was in the market for a new camera (or had money to burn), I'd definitely buy an A7III.
I currently shoot with the original Sony A7 - and I'm very happy with the quality of the stills from that. From what I've seen the still image quality is only very slightly better with this camera.
Where this camera is interesting for me is the beautiful full frame video - and that would save me from having to carry two cameras around (a m43 for video and the Sony for stills).