I'm not sure 14-24 zoom makes too good of sense for Canon. For Nikon, the 14-24 is effectively the replacement for the 14mm prime, and has been said to be of superior image quality to the wide 14mm Nikon Prime. The Canon 14mm prime on the other hand is said to superior to all the aforementioned lenses, including the 16-35 L II, (all third hand information from scouring various reviews, mostly Ken Rockwell). Also the zoom range from 14-24 seem a bit awkward.
Think of what you do with zooms, for me it's to have a bunch of lenses on hand without having to carry/swap them all, and also to be able to get an action shot while it's happening that you would otherwise have missed if you had to move or switch lenses. 14-24 really doesn't seem to fit into that, so what it's utility is, is just going from ultra wide to wide in one lens. I guess that's mildly useful if the 14mm distortion is just too much for your shot, but on the 16 to 35, you go from near ultra-wide, to wide, to near standard and can be used as a walk-around/photo journalism lens. If you stick the 35mm end into your subjects face, you don't get perspective distortion, so it's a nice option to switch to compositionally for many shots, vs. 16mm. 24 on the other hand just doesn't seem to useful because up close, you still get some distortion but it's not exaggerated, and I use my 16-36 normally on the 16 or the 35mm end and 24 is still there if it would prove useful for some situation.
Also, most of the reviews that talk about these various wide-angle lenses, nit-pick minute details to such a major degree, that I barely think it means too much, especially if your handy in post with your digital editing tools. I normally go to here http://photography-on-the.net/forum/showthread.php?t=141406
and just see what people are doing with the actual lenses, taking a large sample of the best pictures offered, and usually what I conclude is, that good photographers take the best pictures, not lenses, as the IQ of most all the L lenses are just phenomenal even for poorly composed/poorly lit/boring shots, and all the hype is just pixel peeping. Pick out the lens for what you want to do with it, not for the minute results someone might criticize or praise it for under an electron microscope. And get really good at digital editing for the small stuff when it really does count.
Personally, if it wouldn't degrade IQ, the only thing I could wish for would be perhaps IS, but I fear that would probably bring the lens into the f/4 category and I don't usually like that trade-off.
p.s. IQ on the 16 - 35 is fantastic, and any minor gripe I've heard of in reviews can be easy removed by a competent digital developer in post, if it's even effecting the image before print to begin with, and I don't find that to be the case from my use. I took this shot with the 16-35 on a 7D at ISO 800 out of the window of my car while stopped in traffic, works for me.http://minus.com/mwi8ith2f