I don't know when Canon plan to update this for the newer, high-resolution bodies (after all, they've updated their 24-70, 70-200, all their superteles and many other lenses) but I know it'll sell like hotcakes.
Cost notwithstanding, a 200-400L or 500L is large, heavy and bulky, and something you'd only take along for a dedicated wildlife shoot. A 100-400L Mk II, on the other hand, is something every travel photographer could pack as part of their regular arsenal.
I agree. Keep it light and compact, and give it 70-300L image quality throughout the range, and I know I'd be in line for it.