Sigma is planning to announce a 24mm f/1.4 DG HSM Art series lens at Photokina with availability coming in October of 2014.
There has been no word on the possible 85mm f/1.4 DG HSM Art or 135mm f/1.8DG HSM Art lenses. I think both the 85 and 135 would be more highly desired than a 24mm prime, though if it’s as good as the 35mm or 50mm, we’ll take it anyway.
I didn't pay attention to this announcement in April, but recently I bought a second hand Canon 24mm f/2.8 to get a taste for 24mm primes, and... fell in love with it. And now I want more!
So I checked out the image quality charts on The Digital Picture.com, but there seems to be little improvement in MTF, going from the Canon f/2.8 to the f/2.8 IS model, see: http://www.the-digital-picture.com/Reviews/ISO-12233-Sample-Crops.aspx?Lens=246&Camera=453&Sample=0&FLI=0&API=0&LensComp=788&CameraComp=0&FLIComp=0&APIComp=0
I agree that handling, AF and IS would be improvements, but not enough to justify the added cost. And for my porposes the 24mm L II is too expensive, for such a specialty lens.
So again I feel I'm in need of a lens that doesn't exist, but may be imminent. So please let it be. Here's me hoping for the 24mm Art to be announced at Photokina in September!!!
In the mean time I think I may sell my 20mm f/1.8 - that focal length is quite close to 24mm and in my experience I don't use the lens all that much because it's too limiting (too wide) for reportage work. I often shoot with a combination of a wide prime (24 or 35mm) on my 5DMkII and a tele-zoom on the MkIII.