Now that the EF 24-70 f/2.8L has been redone, the most requested lens to be replaced with a new version is the Canon EF 100-400 f/4.5-5.6L IS. A few patents exist for a new 100-400, you can see them here and here.
The lens isn’t for an immediate announcement, as we’re told they may be waiting for Nikon to announce the much needed replacement to their 80-400.
We’re told 2 designs currently exist for the lens, and at least one of them has a zoom ring instead of the polarizing “push/pull”. The lens is also said to be weather sealed, slightly faster starting at f/4, a bit heavier than the current version and has the latest and greatest IS system.
This lens could also be considered the IS replacement for the EF 400 f/5.6L, especially if it’s better optically. I’m sure this point may not be what a lot of people wanted to read.
No mention of a timeframe for an announcement. I suspect it’ll be after the 200-400.