I really didn't need to change from the G15 to G16, but the 2 things I mentioned (speed up of AF/reduced lag time and the slightly better sensor) along with the pretty good price for the G16 here in Japan got me to get it. Also, for the last couple of months I had started checking to see if there was anything out there to replace my G15 since things move on since it came out in 2012. Then when I also saw what came out at Photokina I just didn't see anything that was compelling enough. That left the G16 with it's small, but interesting updates. It was much like when I bought the G15 last year. I looked at everything and for my uses decided that the G15 while not ideal was the best compromise. Recently I again examined all the options and ended up deciding that the G16 was the best compromise for me.
After carrying the G16 around here in Sapporo for the last few days I definitely notice the speed up and that is welcome. The G15 was reported to be faster than the G12 (there was no G13 or G14) and now the G16 is even faster. I was generally satisfied with the speed of the G15, but that is in comparison to other digicams. Now the G16 is definitely faster so that focus and lag are closer to using a DSLR. For this sort of camera and the way I use it the speed up is welcome and adequate.
The G16 has a new BSI 1/1.7" sensor that is a bit better than the G15 sensor. Nothing dramatic, but still welcome. A poster on another forum showed full-size raw conversions using ACR. One was at ISO 80 and it was a wide dynamic range, highly detailed photo that looked quite good. He also showed an ISO 12,800 photo in very low light. I was frankly surprised at how good it looked considering the very high ISO and the small sensor. The photo didn't have lots of fine detail to look at such as hair, but the tight, small noise and no banding made me realize that in some situations that this was an ISO that I could use on the G16. Probably better than I remember ISO 1600 or 3200 on APS-C just a few years ago. The new sensor and the excellent state of raw conversion software these days really is rather surprising. The highest ISO photos I have ever shot are ISO 6400 with the A700, Canon 60D, and Olympus E-M5. With the fast G16 lens though I doubt if I would hardly ever find any need to go above ISO 1600.
Just to get an idea of how the new BSI 1/1.7" sensor does compared to the 1" sensor in the RX100 and BSI 1" sensor in the RX100III here are a couple of DxO measurement charts. As you can see, the differences are there, but aren't that large. By the way, what does DxO mean when they say some of the RX100III data points are smoothed? It seems that the tech is improved at a faster rate for smaller sensors.
I have no idea if there will be a G17 or what it will be. With the G7X out now it seems likely that it will have a 1" sensor. Another possibility that sort of sounds attractive to me is if they just have another incremental improvement of the 1/1.7" sensor and manage to speed up the lens by half a stop. The G16 has a fov 28-140mm f1.8-2.8, but the G17 could have a fov 28-140mm f1.5-2.4. I don't know if they could do that, but considering the rather surprising fov 24-100mm f1.8-2.8 for the 1" sensor in the G7X then it seems like it may be possible. The G7X uses a lot of software correction of the lens so that is another thing that the smaller 1/1.7" sensor might need less of.
Anyway, these are just some of my thoughts after a few days with the G16.