We're told that a development announcement for a new EF 800mm f/5.6L IS II can be expected in the fall/late summer. There was even a suggestion that the current version is no longer in production. There was no mention of when that may have ended, nor can we confirm that piece of information.
We've heard previously that a new 800mm was coming and that Canon will be moving it to the new lightweight materials used in the latest versions of the 300,400, 500 and 600mm lenses. There would also be other improvements in optics, autofocus and IS.
If it does come this fall/late summer, expect it before Photokina starts in September.
Canon EF 800mm f/5.6L IS at Amazon