With the D850 announced, it becomes pertinent to ask what Canon has prepared in response.
In the D850, Nikon has a camera with the AF to track fast action with the best of them, the frame rate to not miss the moment, lots of pixels for cropping and enough resolution to do a good job with landscapes (although it may be eclipsed in the latter role sooner rather than later).
Canon has no obvious answer on the horizon. The 5D4, while being the most similar body, is way behind in capability while being around the same price, and would likely be matched by an updated D750 at a far lower price point. The 5D5 isn't due for two more years and would require a huge leap in capability just to match it. The 5Ds is in a different category altogether - it's a slow studio camera that's not great at high ISO (and has limited DR at low ISO) - and any replacement, even if they were to make it a balanced body like the D850, would still have the price issue. Too expensive and the D850 will undercut it, likely by USD1000 or more. Price it competitively and the 5D4 would be pointless, unless they also dropped its price by USD1000.
Will Canon launch a new line (3D)? Elevate the 5D to a higher standard, to match the Nikon? Or will they continue to ignore the competition and live off the momentum and brand loyalty they created 10 years ago and have done little to maintain since? They lost many non-action shooters with the D800 and A7r. The D850 may well do the same for action shooters, if Canon doesn't answer.