I'm just wondering what will the final stable of 50mm lenses be. I find it hard to believe that Canon will keep the 50 1.8, 50 1.4, 50 1.8 IS (or whatever), and the 50 1.2L. Are they going to kill of the nifty fifty and treat the shorty forty as its "replacement," keep the 1.4 for budget wide aperture shooters, and treat the IS model as the non-L intermediate? Now that so many DSLR shooters are on crop sensors, the 50mm length is more like an 80mm short telephoto to them, so the 40mm as entry-level prime lens makes more sense, although a 28mm entry-level prime would be the best.
Also, as to the chorus of "why IS," we've been through this before with the 24, 28, and 35. Obviously they are going to do the same with the 50, and probably the 85. The biggest question left is where they will stop. They already have a 100mm IS macro L that people love, and non-L macro and non-macro 100s. They killed off the 135 non-L soft focus, so that is a possibility, but the 135 L is widely beloved -- would they undercut it with an $800 wide aperture with IS? Seems doubtful. And the 200 L prime -- if they add a non-L with IS, it would seem to undercut the widely beloved 70-200 zooms. Canon has always been reticent to cannibalize their existing sellers (i.e. EOS M vs. micro 4/3). However, as many point out repeatedly, the telephotos are the lengths that benefit most from IS.
EDIT: Oops, I forgot to include the 50mm 2.5 macro. I have a hard time believing that they will continue with five 50mm primes (and a 40mm).