I don't know why some of you complain about corner softness wide open. Do you have any scenario that requires sharp corners using f2.8 except astro, which is the nichest of the niche use? Or 'hand hold landscape'? If you want that, you might as well just get a P&S for the job.
And 24L II is due for an update? Oh please, just cut it.
When you shoot at f1.4, or f2.8 for that matter, you want your point of interest to be sharp and in focus, and you want your background, that includes the corner, to fade away to reinforce the attention of the topic. And how many of you puts your topic object in the corner and shoot wide open? Let say 0.0001%? And in normal usage, wide open in center / mid-frame, 24L II is the sharpest f1.4 lens I've ever used.
To me the versatility of 16-35 trunces the bulb head 14-24. The useful 35mm f2.8 setting (not many UWA offers that), the flare resistance as mentioned above, the ability to take filter are all better. Which includes putting on a UV filter and don't worry about using it in harsh conditions. I've seen so many 14-24 owners bought the lens, gets excited, then put it in storage because they don't want to make undue damage to the bulb head front element. How sad.
Even if Canon comes up with a bulb head 14-24 I'm sure I won't be interested. By switching my 16-35 to a 14-24 I will have to buy a separate 35mm lens, double dent in the wallet!