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, Sony α6000, G16 | EF: SY14/2.8, V20/3.5, 28/2.8 IS, Ʃ35/1.4, 50/1.8, 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, 70-300L IS, T28-300 Di VC PZD, Ʃ150-600 DG OS HSM S | E: SY12/2, 35/1.8 OSS, 16-70 ZA OSS, 55-210 OSS, SY300/6.3 ED UMC CS