It's been suggested that Canon will indeed update the 100-400, but not just with IS. Howabout an extra 100mm.
The Sigma 50-500 is giant at f/6.3, not sure how big 5.6 would have to be. Could Canon keep a lens like this in the $2000 range and a bit lower?
This rumor has been debunked for technical reasons. I think I'll stop posting EVERY email i get.