I just dug out the first reference to the updated 100-400L here on CR. It was the 7th post on the then-new CR blog, and suggeted the lens would be announced at PMA...in
2008.
http://www.canonrumors.com/2008/01/canon-ef-s-17-200-f35-56-is/
The same post predicted the EF-S 17-200 lens for the 2008 PMA, and while that didn't happen either, the EF-S 18-200 was announced just before Photokina later in 2008.
Of course, rumors of the 100-400 II predate the CR site by several years...