Is there really a need for Canon to develop or redesign lenses that are faster than f/4? Given the surge to digital, such a dev track may not make much economic sense. Sensor technology is only going to get better. Noise at higher 'ISO' (I'd prefer if this vestige from film were tossed and replaced with something like 'gain' which is more accurate) levels is gradually improving. Therefore, the differences in shooting at ISO 100 or ISO 400 are relatively minor and easily compensated for in software if needed. It may be that lenses that are faster than f/4 will be called 'film lenses' in the near future because they really aren't needed in the digital marketplace except as niche items as opposed to mainstream.
One good reason for a faster lens is to get a brighter image in the viewfinder. Especially since many modern digital SLR's use a cheap penta-mirror rather than a penta-prism. An APS sensor means a dimmer image too. Personally I am happy with F4.