Good comment regarding the MTF information with the 1.4x attached. It looks very good on the MTF, but I hadn't thought about the diffraction at f8 keeping you from attaining the theoretical. At f8 that is only getting started, so I'll keep my fingers crossed. I'm still hoping that the resulting 560mm will be better than the 400mm I'm getting on the 70-200. If the testing shows it isn't, then that will probably cause an all stop on the changes I'm making on the long end of my kit. Depends how good it is with just the lens.
Bear in mind that as good as the 70-200 II is, when used with a 2x TC and a 1.6x crop body, the end result is much the same as using a 3.2x TC. That is really pushing it. I'd be willing to put money on the 100-400 at full zoom on a 1.6x body being much better.
Even with a 1.4x TC on the 100-400 and the 1.6x crop factor, it's a lower 2.24x magnification. Still pretty radical expecting to get ~900mm out of a 400mm lens, but it's much closer to sensible limits than 3.2x.
Diffraction is possibly the most predictable form of aberration out there, and mild forms of it (which you'd get with a 1.4x TC even wide open) could possibly be largely overcome with a very mild amount of sharpening in PP.
If you're uncertain, I'd suggest waiting for the digital pictures test chart shots of the lens, hopefully with this body too. Certainly looking at the standard lens to compare bodies, the 200/2, when set the f5.6, there's hardly any resolving difference between a 7D II and a 6D. Big difference between a 7D II and 7D. Let's hope he uses the 7D II as the standard crop body to test with from now on, and does the 100-400 II with/without TC's with that.