...maybe give us a non-DO 400 f/4 for the masses...
I'm not sure why this keeps coming up...a non-DO 400/4 will be the same diameter and a bit longer than the 200/2. It won't be 'for the masses,' unless you think 'the masses' can afford a lens that will cost well over $6,000. An 'affordable' 400mm lens will have an f/5.6 aperture, and there are two already (100-400L and 400/5.6), and hopefully we'll see updates to both soon.
+1, and the 300mm f/2.8 II + 1.4xTC III is a supersharp 420/4 lens already, second only to the incredible 400/2.8 II
5D IV, 5DS R, 7D II, EOS-M, Powershot G3 X, 400mm DO II, 300/2.8 II, 1.4xTC III, 2xTC III, EF 1.8 STM, EF 70-200/4 IS, EF 24-105, 15-85, 100-400 II, Sigma 10-20, Sigma 150-600mm C, EOS-M5 15-45, f/2 22, 11-22, Samyang 8mm f/2.8 fisheye