I had the G1X II, which I used with my 5DIII + L's setup as a personal camera with the 5DIII for events and special occasions, and ended up switching to an EOS M3 +EF-M setup due to a growing young family made the big setup too bulky and the G1X II although great, the wife complained the photos weren't good enough, which I'd agree so the M3 is a great compromise on size, but without sacrificing IQ.
But, Canon has the means to produce a truly masterful upgrade for the G1X III since it was released 3 years ago, addressing all of it's shortfalls... Here's my wishlist...
18MP Cropped 80D sensor w/ADC and DPAF (24MP APS-c x .79 IE 1.5" crop of the wafer); DR was/is a real issue on the G1X II, resolution never was, but they can do 18MP, why not?
24-120 IS BR (the lens on the G1X II suffers some considerable CA, which Canon admits learning from when designing the G7X lens, if they could do a BR variant, it'd cure lots of evils...)
DIGIC 7 processor thus 8FPS RAW and JPG
Updated Firmware (the Powershot firmware leaned to wide open on Auto and P, plus high shutters in low light, both required Manual to get it quite right which took a lot of fun out of street shooting)
4K would be nice, but even 1080 @ 60FPS with higher bitrate would be wonderful
Built-in G5X style iEVF
Built-in extended grip (GR-DC1A or better, my M3 grip)
G5X / M3 /G7X dials, IE an exposure comp, and maybe the selection lever, helps if you need to use manual, which you want to, quickly.
I'd be in hog heaven if they did the above. I'd even consider going back to my PowerShot G + 5D setup if they did. The trouble is they need something lightweight, that can punch a little harder than the G5X can; it impresses me, but the IQ doesn't even come close to my G1X II or M3 between that mushy 24-100 lens and 1" sensor they got on it.