Source told that the new Canon EF 800mm f/5.6L IS II USM lens is coming. The 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 800mm f/5.6 VR coming down the pipeline, this lens is in use during the London Olympics. This lens barely felt heavier than the new Canon EF 500mm f/4L IS II which weighs in at a hair over 7 lbs. 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.