So, what range of 300 f/2.8 incorporated into a zoom do you see it being then (assuming that part of the rumour might be real)?
Personally, the 35-350L was the first white Canon lens I bought (a long time ago), and while its quality is passed by any white prime and almost any shorter range zoom too, it wasn't useless, and is a great safari lens when you don't know what range you need and can't change lenses easily due to dust and bouncing in the back of a landrover
Given the direction of some recent lenses, I wouldn't rule a super zoom out (though not at a fixed 2.8 aperture, mind you).