One thing to consider Shadow is I spose that rumours around the D850 were VERY thin on the ground before the lead up to the release. We had assumptions that it would use the D5 AF system but the combination of very high resolution AND high FPS is not something I recall ever being mentioned, at most some people were expecting it to stay at 36 MP and maybe up FPS to 6-7. That could mean that Canon themselves did not know what Nikon was going to come out with which could delay any response.
I'v seen a lot of talk saying the D850 isn't really a revolutionary camera because its combining a lot of existing tech with a decent(but not massive) resolution bump. Whilst you could counter that specifically with the speed/resolution combination to me whats perhaps even more significantly is that it seems to represent a shift in mentality for bodies at this level. Previously there was I'd say always somewhat of the feeling you were dealing with releases that were intentionally limited to either avoid cannibalising sales of flagship bodies or were holding back leaving room for a future update. This camera on the other hand seems like more of a case of Nikon throwing everything it has into the body besides perhaps build(relative to the D5) so again perhaps something likely to catch rivals on the hop?
The language coming out of Nikon after the DL debacle did seem to point at significant changes in there corporate mentality. The 1 series mirrorless bodies for example were for many THE classic case of a product sabotaged by trying to avoid cannibalisation of its existing business.
It's a revolutionary design. The individual parts are not (AF system from the D5, sensor which likely isn't too different from other sensors Sony has put out recently, etc.), but when combined, bring capabilities that have never previously existed in a commercially-available camera. No other camera combines the AF of a top-tier camera with a full-frame sensor that has as high a pixel density as a contemporary crop sensor (i.e. leaving no reach advantage to the crop body, while giving the new camera much more cropping flexibility), while being capable of shooting in the 8-10fps range required of a sports or wildlife camera. Prior to this, the closest we had was the 5D4, but that doesn't have quite the frame rate of an action camera, nor the resolution needed to completely negate the reach advantage of a crop sensor.
I think what may be emerging is a realisation that the pro market isn't a monolithic block of sports photographers who just want speed, speed and more speed. There are also those who need resolution, resolution and more resolution (and some DR) - commercial/studio/advertising photographers (some of whom previously shot digital MF), real estate photographers, those shooting backdrops and textures for TV, cinema, VR and other SFX, etc. Then there are those who need a balance - field sports, wildlife documentary and others (typically operating at longer focal lengths) who need sufficient resolution as wel as sufficient speed, as well as photojournalists and other general/all-subject photographers who need a do-everything body (or a pair of them) rather than something that specialises too much at one end, at the expense of the other. And, increasingly, they may be realising that, just because these groups don't require the frame rates of the speed-focused photographers doesn't mean that they don't need the same AF, build and other features of the top bodies. Just as importantly, the technology, especially in terms of data handling speed, now allows it - if you can make a 24MP/20fps body, as well as a 24MP crop sensor, you can also make a 48MP/10fps full-frame body. And all these capabilities are necessary to reach the next milestone of an 8k video camera (39MP at a minimum 25fps, if keeping the 3:2 aspect ratio), so they do not represent wasted effort catering to photographers alone.
There have always been three basic groups of requirements among those wanting top-tier bodies - speed-focused, balanced speed and resolution, and resolution-focused. Even in the film days, this would have been represented by 35mm cameras with motor drive systems (speed), the same 35mm camera without the motor drive (balanced) and medium-format film. There is also often overlap between the groups - a sports photographer will also often want a balanced second body for longer-distance shots or sports played on larger fields, while a resolution-focused photographer will often also want a balanced second body for occasional action use. So far, the speed-focused group has been very well served, but the other groups have been somewhat neglected since the demise of the D3x and 1Ds3 (both resolution-only) and D700 (balanced) bodies, having to rely on bodies with second-tier AF capabilities in order to meet the resolution and frame rate requirements. This is obviously more of a problem for the balanced group than the resolution-focused group, since the latter are likely to be shooting static subjects anyway. The D850 elevates the balanced group to the top tier again. I would guess that the 5Ds2 would do the same for the resolution-focused group, since it will almost certainly have a higher resolution than the 5Ds (and, by definition, the D850); seeing the D850, Canon still has time to put a 1Dx2-level AF system into it to remain competitive, even if they had been intending to use a 5D4-level system. Getting blindsided by the D850 is one thing (I believe Canon were blindsided by the initial D800, or, at the very least, knew about it but were in no position to compete against it). Getting blindsided and then being stubborn enough to ignore it is a whole new level of stupidity. I would say that Sony's next few releases will also do the same, at least for the A7r2 replacement (using the A9 AF system) in the 'resolution-focused' group, and possibly a 'balanced' body as well - unlike Canon, there's little chance that Sony didn't know what Nikon was up to, since they made their sensor!
