What I'd most like to see is a line of EF-S prime lenses, starting with about a 14–18mm pancake.
Longer ef-s primes won't happen because you can just plug a shorter ef lens and use it with the 1.6x crop factor, the smaller aps-c mirror is only an advantage for wide angle lenses.
As for wa/uwa ef-s prime, imho that won't happen either because ef-s is either for amateurs who are supposed to be happy with zooms or for people who want to use tele lenses for more reach...
Just wait till Samyang brings the 10/2.8 UMC for APS-C
50mm F/1.4 USM II
+1 ... but the reason why this didn't happen yet might be to protect the sales of the expensive 50/1.2, if the 50/1.4 gets any better with a "real" usm drive there'll be little reason to buy the good-bokeh mediocre-sharpness L - so probably they'll either replace both or none.
Actually, I would be much more interested in 50/2 IS USM Macro, or even a cheap 50/1.8 STM. I think that the rest of Sigma's prime "jewels" (50/1.4 and 85/1.4) will be reborn into A series pretty soon, and only after that ... Canon will be forced to do something about it.