A new-and-improved 100-400?
This lens is loooong overdue and would likely sell like hotcakes, as did the current version. I was recently looking at Nikon and they have a new improved version of their 80-400 and the reviews are off-the-charts positive. The improved Canon would need zoom ring instead of push pull and preferably start at 80mm instead of 100mm to match Sigma and Nikon.
I would be very happy with a 100-400 f/4