Rumors for a 24mm f/1.4 Art have been rampant for months. In my opinion, a modernized 24mm f/1.8 EX with Optical Stabilization (and HSM, needless to say) makes just as much sense.
Let me elaborate a bit further:
- In this range, the competition makes f/2.8 lenses (both stabilized and non-stabilized, quite affordable), f/1.4 lenses (non-stabilized, usually very expensive), and a few unique optics with no stabilization (Zeiss 25mm f/2). A 24mm f/1.8 OS option would offer a good balance between speed, size and price ($799?), with OS to boot.
- The super fast f/1.4 speed is probably less sought-after at 24mm than at longer focal lengths. Also, a 24mm f/1.8 is less difficult to design than a 24mm f/1.4 (see Q/A below). Field curvature and the various optical aberrations are a pain to correct with any f/1.4 lens, but the wider the focal length, the more difficult it is. So whether it is worth the effort or not is a tough decision.
- As a bonus, the video market should respond favorably to a fast and stabilized wide-angle lens.