After some interesting comments seen about the age of the current EF 100-400 f/4-5.6L IS tele-zoom from Canon (for example, in the recent test done by Chasseur d’Images), there is now an active rumour about the arrival of a real replacement.
The Canon EF 100-400 f/4-5.6L IS II would no longer be a push-pull design but would have a second ring (like the recently presented Sony design). Better for managing the sealing and protection that are so important when used in difficult conditions like a photo-safari. It would also be equipped with an upgraded image stabilizer (the most critical issue with the existing zoom).
Expect a price of US$1700. If that one is true, it will be a very good price.
Announcement: Not sure, but you can bet there would be something about it on September 17th when Canon will present its new SLR body.
Via Canon Rumours.