Since a decent number of people have only f/2.8 and faster lenses, why not a variant of some existing models with f/2 and f/2.8 AF sensors instead of the f/2.8 and f/5.6 AF sensors currently used?
I'd like to say f/1.4 and f/2.8 AF sensors instead (2 stops apart, just like the f/2.8 and f/5.6 AF sensors currently used), but then the 85 / 1.8, 100 / 2, and 135 / 2 woudn't see any benefit, and going f/1.4 and f/2 AF sensors would exclude all the macro lenses, as well as many of the popular fast zooms.
Would such a move be unprofitable? That is, we have no choice but to get the bodies with the current AF sensors, so what's the incentive to go to the effort to give us a choice? Or might it not improve the AF speed/accuracy enough to maybe convince at least enough of the people Canon has lost to Nikon to come back and be a profitable move?