Wouldn't this sort of sensor be incredibly helpful for sports/action?
Nope - we expose our images properly.
Epitome of lack of critical thought here, especially from someone implying they are a sports/action photographer. Sometimes the light is really low, where the only way to get a reasonable shutter speed is to underexpose. Some photographers cannot afford fast lenses, so their only option would be to underexpose to get proper shutter speeds.
So, no other way to put it, but you are flat out undeniably wrong. This sort of sensor would be incredibly helpful for very many sports/action photographers.
Speaking of a lack of critical thought...when the light is so very low, do you usually find yourself shooting action at ISO 100? At ISO 400? Or have you raised your ISO higher than that...where the differences between Canon and Exmor sensors have evaporated (or the Canon sensor has the advantage)? (BTW, I trust someone so knowledgable as yourself won't bother bringing up the a7S in the context of sports/action).
Even if the cameras are comparable at higher ISOs, having one that performs better at lower ISOs is always a nice thing to have. Think of it as an extra feature added in for free such that you don't just have IQ performance comparable to Canon's but better.
The IQ isn't better unless you need a lot of extra DR at low ISO, which is hardly necessary for most photographers. And for that extra DR you are trading for a camera that is still lesser in a lot of areas than the more than two year older Canon. And what about lenses? Also a better flash system. Does this new Nikon have a better AF system than the past, or is it the same 51 point and less than 20 cross type sensors?
"Most photographers". I love that term. How do you know what "most photographers" need? Have you surveyed them?
Unfortunately flickr doesn't do ranking on ISO (and nor will Google be able to do search results for that either.) However I suspect that there will be more pictures rated ISO 100-400 than there are at (say) 1600-6400.
Yes "most photographers" expose correctly no matter the ISO. My 1DX or 5D3 ISO 100 images will have the same great IQ (but better colors IMO) as the Nikon because it is exposed correctly and captures all the DR I need. And most photographers do the same. It is a rare case that I need more DR and would not sacrifice any of the other features the Canon excels at for a little extra low ISO DR latitude. That is the only noticeable benefit of the Sony sensor.