Back to topic, as I suggested. There probably wont be a 5DS R II till tale in 2018. So yes, canon has no real response.
The question is how long they can be successful business wise with good products but products that are significantly behind those of their 2 main competitors along most important metrics. Factually, it's been like that for years on the bodies for photography applications (not for video obviously) but, more worryingly for Canon, they have IMHO been losing on the lens front as well. They do of course still have a great line up covering the needs of pros very very well, but their choices of lens roadmap and lens design technical options follows the same philosophy as their cameras: reliable, relevant and good but boring and lacking vision, ambition and character/excitement (we'll see if the 135mm T/S indicates a shift in the right direction or is a anomaly). They seem to be shooting for a Toyota like market positioning but with a 10 years delay and without the Lexus brand equivalent, effective but average. I am not sure this is the right choice when you see the urge of photographers to differentiate themselves.
Canon and Nikon have somehow been switching position these past 5 years. Canon used to do the 85mm f1.2 and Nikon their middle of the road 85mm f1.4... these days Nikon releases their 105mm f1.4 while Canon comes up with a 85mm f1.4...
The fun part comes next though... Odds are that Nikon will release a breakthrough FF mirrorless body in the next 6 months after they have convinced their DSLR use base to buy a historic amount of D850 bodies. The D850 is the digital F6, the last body DSLR users will need before Nikon moves on to next gen. And that is going when the real trouble may start for Canon if they continue acting the same.
Per my, reasonably educated, guess, Nikon's mirrorless is going to be very high end, a digital rangefinder produced in Sendai with a new range of very high performance lenses and an adapter with embedded AF module enabling to focus their current range of lenses with excellent AF performance.
Cheers,
Bernard