I would also like to see an updated 17-40/4L (or a 16-35/4L), hopefully with IS, but most imported with high optical quality.
IS versions usually require a larger filter size (front element), that's supposedly why the 24-70/4 has IS and the 24-70/2.8 hasn't. For the 17-40L with 77mm now this might still work, but for the 82mm 16-35L it could be tricky.
In any case if the corner iq is also improved you'd probably see more weight and certainly a massively "improved" price tag. The question is if the 17-40L mk2 could still be the L budget choice - and if you want heavier and better, you can get the current 16-35L right now.
Nikon have a 16-35/4 VR, http://imaging.nikon.com/lineup/lens/zoom/widezoom/af-s_nikkor16-35mmf_4d_ed_vr/index.htm, with 77mm filter size. The 16-35/2.8L II that I have seen, have not that good optical quality in the corners.
Canon can keep the current 17-40/4L as a budget lens, and still have a sharp (more expensive) 17-40/4L (or 16-35/4L) as they do with the 70-200/4L and 70-200/4L IS, I think that is exist a demand for both of them...