I now do exactly that with my YI360.
Photo over video (compression artifacts)
BUT, as @4004 mentioned in one of hit points the quality of the extracted images is noticeably less then form a single taken image. My YI360 is a 5.7k camera. When I take an image the file size is something like 9Mb. When I extract an image from a video file it is around 3Mb. The video and image both at maximum quality settings. The difference in file size is huge and yes when zooming in you see that although both images have the same amount of pixels, the quality is noticeably less good.
I do think the quality of image grabbing will be better from the QooCam. One reason is obvious, 8k is quite a bit more then 5.7k. BUT also I can set my YI360 to a maximum video bitrate of 120 Mbps. I have read that the QooCam can be set to 200Mbps, therefore chances are that the quality difference between an image and a ‘video grab’ will be at a more acceptable level.
Power consumption
Assuming that cameras most likely are comparable to certain degree I do not think the power consumption will differ a lot. In video mode, when I set the camera to one or two image every seconds or in full video mode, the battery life time remains more or less equal. I am not (yet) able to get the YI360 in an image-interval-mode… but I expect the battery will be about the same.
Processing & no raw/dng
For mapillary I’dd advise to use automation when you want to go into the serious numbers of images. Grabbing images from a video file is quite doable in automation, so in my opinion not much of a hindrance. That is also why raw/dng in video won’t be missed I think. In that format you can fine tune an image. Great when you want the perfect result for every single image, but as good as impossible to automate…
available space
Well, when you’re serious in making a lot of images those las few bucks spending on a large SD card won’t stop you I think, the gain in (potential) quality and ease of use will win every time.
I bought a (fast!) 128Gb card… but even on a whole day of taking images I barely needed half… so I’dd advise to buy the fastest 64Gb card you can find 
memory bandwidth
As written above, get the fastest one you can get! I am quite curious how much better image grabs are at 200Mbps (as to my max of 120Mbps, it is 2/3 more data!) And I’m quite curious as to how fast the QooCam can take images… chances are that (when the software supports it…) you can take images fast enough when walking and hopefully when cycling. When you attach it on the roof of your car you’ll need to revert to the video grabbing I think. In the end (assuming the camera can be reconfigured to the extreme) it will become a trade-off between image frequency and quality.
Personally I wouldn’t mind if my/the camera would have the option to increase the Mbps to say 400 or even 800 Mbps resulting in say a maximum image rate of once per second to once per two seconds (ideally, let me dream for a sec ). I’dd have a sequence in one file and have the quality of image.