plus one... how can the 200mm f/2L IS be made better?
+1, only possible way is to lower its weight, but a 200/2 will never be light for a 200mm lens.
A lot of people thought the previous crop of 300, 400, 500, and 600mm lenses couldn't be made better. In every respect, including and in particular IQ, all of those Mark II lenses ARE better than their predecessors. Sometimes by a significant degree. For example, the new EF 600mm f/4 L IS II is sharper than the EF 800mm f/5.6 L IS, even when a 1.4x TC is used, according to a review by Art Moriss
, a world-renown bird photographer who puts his gear through the greatest of tests every time he uses them. In another article
, Art also notes that he will be moving from the 800mm to the 600mm thanks to the fact that it is overall, in pretty much every way, a better lens (closer MFD, better sharpness, lighter weight, etc. etc.) If you read through his blog, he has quite a few good things to say about the new generation of telephoto lenses from Canon.
I see no reason the 200mm f/2 and the 800mm f/5.6 couldn't be updated to be just as superior to the current versions as the new generation of recently released Mark II lenses are to their predecessors. Lighter, better IS, faster AF, significantly improved center to corner sharpness, etc.