Computer screen resolutions will also keep getting higher,
With 16mp on my retina macbook when I have a 16mp original image, applying 1.8 crop factor on that image already gives me a 100% crop on my screen (leaves around a 5mp image).
So when the image is not 100% focused, even a 16mp image can look so so on my screen, when I used the d800, even some poor focused images still looked sharp (ok).
Applying the 1.8 crop on a 36 mp image still leaves you with a 11.1 mp image.
For printing and photo books it doesn't really matter. , but I did quite like that the more MP masks my poor skills at times
, also for action shots it can have some benefits. I rather shoot with 300mm f2.8 and 44mp than 500mm f4 and 16mp, It's a lot easier to track with a small portion of the viewfinder filled than almost the entire viewfinder!, also nice to have both the close up and overview shot in 1 go. However at this point the fps are still a bit of a problem, 4fps is not quite enough, if they can manage to get that to 6-7 fps it would be great.
I also wonder how it will affect auto focus, since it's harder to keep auto focus point on the target.
It is a bit like having 16mp file and a 7mp image on a full hd screen (around 2mp screen), or a 36mp and 16mp image on a 5mp screen.
If you have a 7mp image to start with on a 2mp screen there is also not a lot of room for focus error or cropping afterwards.
So as (computer) screens keep getting more pixels, I would personally not mind having 40+mp cameras