I think a 24-105 F2.8L IS USM would kill the market for the 24-70 F2.8L II. I am not so sure if it would do so much for other lenses. I would still like to use my 50mm F1.4, and I will never stop using my 135mm F2.0L for any lens:)
My 24-105 and 70-300L are my walkabouts, the 135 is my favourite prime which I use for portraits of humans and animals.
A 24-105 fits nicely onto a 1.3 and ff so I would get one