I'm starting to think this lens is a bit too much of a swiss pocket knife. Too many features, too little space.
I think it would be beneficial to drop the built-in TC as mentioned earlier. It's nice as a commercial stunt, but a 200-400 without it will be more reliable and most likely sell more units, especially if it's priced to beat the Nikon version.
5D3, 5D2, G5X, G16 | SY14/2.8, V20/3.5, 28/2.8 IS, Ʃ35/1.4, 50/1.8, 50/1.8 STM, Ʃ50/1.4 EX, 100/2.8L IS Macro, 16-35/4L IS, 24-105/4L IS, 70-200/2.8L IS II, 1.4x II, 2.0x III, T28-300 VC PZD, 70-300L IS, Ʃ150-600 OS HSM S