Yes, you read it right.
Canon has announced it is developing the EF 200-400mm f/4L IS USM Extender 1.4x lens.
More here:
http://www.dpreview.com/news/1102/11...on200400mm.asp
http://www.canon.com/news/2011/feb07e.html
The in-built extender turns the lens into a 280-560/5.6. I can see this lens being enormously popular for sports and wildlife photographers.