The new 16-35L is an interesting option for me. I'm in the market for a UWA but I don't use tripods enough to justify a 17 TSE. 14L is a no go.
If performance follows I might be in for a trip to the shop. Getting used back to f4 as max aperture will be awkward tho...
Waiting on reviews.
PS: extra points for the non extending design. it's kinda OCD but this is a real turn off for me. The only thing I'd change in the 24-70.
Yes, I do think the new 16-35mm L will be interesting for many people. The MTF chart http://www.usa.canon.com/cusa/consumer/products/cameras/ef_lens_lineup/ef_16_35mm_f_4l_is_usm
indicates that it’s definitely a sharp corner to corner UWA, yes - also at the wide end - wide open still really quite good.
Indeed - I understand what you mean about being unable to justify a 17 TSE. I initially bought a Sigma 10-20mm f/4-5.6 back when there were only a few options for APS-C UWAs. It served me well for some years - and I bought it new, at a good price (half the price of the Canon 10-22mm). However last year when I tried the Sigma 8-16mm I was sold (and the price of this ultra UWA was lower than when it initially came out). The 8-16mm is definitely sharper, has noticeably less CA - and importantly translates to about 3.5 mm wider (in 35mm / FF format), which is very noticeable.
I expect the 16-35mm f/4 L will have some of the same benefits - sharper (esp in the corners), possibly less CA and has IS (which while not the absolute most necessary feature of a UWA, is certainly useful and even at times highly desirable).
While f/4 is not fast, I don't have a need for a fast UWA. When I want fast, I want really 'fast' (I don't consider f/2.8 'fast') - so I want primes between f/1.4 and f/2. I expect that for many photos that FF shooters will use the 16-35mm f/4 L for, it will be between f/8 and f/11 anyway. And the same for the EF-S 10-18mm f/4.5-5.6 STM too. (I am still very impressed by the price of the 10-18mm lens... just $299 new... incredible!)
I also prefer lenses that don't extend, but it's not the most important criteria for me (I have some good lenses that do extend, eg the Canon EF 70-300mm f/4-5.6 L IS USM, and the Canon EF-S 15-85mm IS USM.