Fifty megapixels is a big deal.
From what I see the Canon 5DS R easily matches or beats the Leica M Monochrom Typ 246 while offering vastly superior monochrome conversion options, and handily outperforms the Canon 5D Mark III with superior resolution and greatly reduced aliasing.
Shown on this page are comparisons at native resolution, 12000 pixels upsampled for all, 7360 pixels resampled for all (D810 res), 6000 and 5760 pixels resampled for all. In total, a revealing performance tells the tale of just how awesome oversampling can be. I look forward to a 144 megapixel DSLR.
Also apparent is that the Zeiss Otus 85mm f/1.4 APO-Planar has a lot of room for growth in sensor resolution. Heck, it’s good enough wide open at f/1.4 for 50 megapixels (not optimal at f/1.4 but beyond reproach). So go get your Zeiss Otus 85/1.4 APO-Planar and its Zeiss Otus 55mm f/1.4 APO-Distagon sibling. Because you’re just scratching your ass with most other lenses on the 5DS R.