It may finally be on its way
Canon EF 200-400 f/4L IS 1.4x is consistently a lens I get asked about. Canon announced the development of the lens about 18 months ago and hasn't spoken much about it since.
Mike Owen, a communications manager for Canon said they expect to have the lens available before the end of 2012. Although he wouldn't commit to the date.
Some loose specifications about the lens?
It's expected the EF 200-400 f/4L IS 1.4x will weigh slightly more than the new EF 400 f/2.8L II, which weighs in at 3.6KG. Minimum focusing distance of the big lens is 2 meters and has focus limiters 2m-6m and 5m to infinity. The lens also comes with a PF, or power focus mode for smooth focusing during video shooting. Another neat fact is the 1.4 built in extender actually comes from Canon's broadcast lens business.
The retail cost of this lens? The last we heard, it'll come in around $10,000 USD.