I hope Canon is not going to make the same not very smart move like Nikon: 200-500 with better AF engine and at least slightly better quality control (I have no idea how much it will increase the price but at least the engine shouldn't be that much expensive. The quality control is expensive!) would be really something. I have good copy (as an IQ) but it's slow!
Did I say SLOW? I understand that such a lens will compete with it's more expensive sisters but there is also another stuff that is going into considerations when one compares them... And when buying them! 200-500 f5.6 is readily available 24/7! The 2.5x more expensive 500 PF is still in back-order - despite at least in the center it's not much better (but even the corners are not that much better and when you are taking photos of wild life the corners not always matter...).
OK - but what about the resolution when you shoot longer distances? What about AF speed and tracking abilities? What about the weight? Off-course the zoom has the advantage to be zoom but I found myself shooting mostly at 500mm... And what about working with converters?
I really hope Canon will make it the right way (and still money effective!) - just look at the 100-400 last generation, they have a tradition there!