I used to wish that, but then, I woke up.I wish I could say "Go for the uber sharp 14-24L", but..
The 17-40 is rubbish, and the 16-35 is more of a workhorse for photojurnalists. Sharp at the center but lousy edges and corners.
If I were you, I would go for the Zeiss 21mm, or for the 17mm or 24mm TS-E.
Personally, I'm waitng for canon to release a better UWA-zoom for landscapers. I don't care if it is 14-24, 16-35 or 17-40. I just want it to be razor sharp across the whole frame.
+1....razor sharp at f2.8 + IS for handheld slow shooting.
Now I have all 3 mentioned primes. I bought one every year for the last 3 years.