And what about 14mm f/2.8, which is already there?
I also wanted that Canon make 14-24 f/2.8, but then I thought, would I really miss that range between 15 - 23 mm, if I buy 14mm f/2.8. Actually now I don't have money to buy it, but if they won't make 14-24 f/2.8, I will probably buy 14mm which already exist. I also didn't read any tests about that lens yet, so I don't know if it has any weak points.
I'd rather have f/2.8 than f/4 on a UWA lens, because of shooting night skies.