The 14-24mm was on my wish list. But instead I bought the 16-35 II
I actually like the range 16-35. It suites me well as landscape / walkaround and indoor lens. The thing that could be improved though is the sharpness at 2.8 in 16 to 24 mm. There are other things like some vignetting at 16mm but those can be taken care of in post-processing.
I think there is room in the market for both, a 12/14-24 f2.8 and a 16-35III 2.8.
The first lens will certainly have a bulbous front element and therefore be a pain with filters, which make lanscape work a pain the back side. Polarisers and NDs are pretty much precluded unless the filter sizes become huge and therefore unmanagable in the field.
The 16-35 is a compromise lens, it does a lot well but not spectacularly well. It's very wide, but these days there is wider. It's not too corrected but just enough so that post prod correction is effective. It's a useful range and quite sharp....but it could be sharper. Although it's sharp enough for most applications, there will always be some sharpess monkey out there who claims it's not sharp enough. It takes filters very very well and it's easily the most versatile wide lens. Unfortunatly it flares and ghosts quite a bit and could do with an improvement. It's weather sealed and it's easy to wipe water off the front element (or front filter), where as one rain drop on the front of a TS-e 17 is hard to remove and is massive on the final image.
If the 16-35 front element gets damaged (and I've had mine replaced) then it's expensive...but not as expensive or vaulrable as a big front bulging element.
For regular pro work, the 16-35IIL is currently the best choice. It's hardy, versatile and sharp enough. I think a 12/14-24 is more of a fan boy dream...usefull for shooting charts and not so usefull in the real pro use arena. Imagine taking a 12/14-24 to a war zone? Hell, even Cornwall UK on a windy rainy day would render this lens useless.