I dont see it happening. While it would be nice, one would think Canon would have had some sort of announcement at NAB to start the hype. I dont think we will see anything until the first of the year at the earliest.
Canon doesn't use NAB to make anouncements for it's prosumer equipment. They have always used DVExpo East to make their announcements and introductions.
However, I do agree that it will probably late in the year before anything will be said. Even then, it probably won't be until 2006 before you "see" anything.
While its all speculative and pretty much pointless to debate, they kept things pretty much hush-hush on the XL2 until the last moments. I don't see them as tipping their hand this early by making an announcement at NAB and loosing out on sales of the XL2 between now and whenever they get around to releasing an HD cam. It would have been a foolish move on their part to start spouting off about their next incarnation of the XL.