Replacement of the big one?
I have been told on a few occasions that a replacement of the EF 800 f/5.6L IS is coming. An announcement could come as early as late Q1/Q2 of 2013. The new lens would incorporate Canon's new weight saving technology.
Nikon has an 800 f/5.6 VR coming down the pipeline, and I spoked with someone that had a chance to handle the lens in London during the Olympics. He mentioned that the lens barely felt heavier than the new Canon EF 500 f/4L IS II which weighs in at a hair over 7lbs. If true, that would be pretty great, as the current Canon EF 800 f/5.6L IS weighs in at 9.9lbs.
Another sign that a new 800 may be on the way is the lens hood ET-155 has been discontinued by Canon. This hood was also used on the Canon EF 400 f/2.8L IS, and that lens has since been replaced. I know of the discontinuation as I have had one backordered from Canon for nearly 6 months. B&H Photo just informed me today that the lens hood is no longer available. Canon still lists the ET-155 as the lens hood for the 800. I will try the ET-155WII, which comes with the new EF 400 f/2.8L IS II and see if it fits.