What's crazy to me is that no one mentions the tokina 16-28. It was on sale recently for $699!!!!! Crazy cheap and has gotten very favorable reviews. I don't know if this dream 14-24 canon lens will out-resolve the Tok 16-28, if the Canon lens is even a reality.
14mm is WIDE!! So wide, for me, that you literally see little detail in the distant horizon. Nearly Too wide, for me. 17-20mm is my preferred FL, which my 17-40L quits distorting at around 19-20mm anyway. I've never needed WIDER, but many times needed sharper. If the Canon cannot accept filters, then it gets a thumbs down for me. On a bright sunny day, this lens becomes a lot less practical. At dusk and dawn (magic hours) I believe you can get by without filters.
If it does accept filters, then that opens up another thick, juicy layer of opportunities. If I had enough disposable income it would go to a good tilt/shift. One thing I haven't considered: at some point in time I would LOVE a 1d4. So the math gives me 14*1.3= 18mm & 24*1.3=31mm. Hmmm, pretty useful for me.