100mm f1.0 = 10 cm lens diameter same as the 200mm f2.0. Are you sure you wanna carry that? 100mm f/2 from canon is a good alternative, no? What about using TC 1.4X ?
Yes I want to carry that! It wouldn't be much heavier than a 70-200 f/2.8. I wouldn't say the 100 f/2 is a good alternative to such a mythical lens, no (is the 70-200 f/4 a good alternative to the 200 f/2? Not really, optics-wise anyway!)
But like I said above, I've considered trying the 100 f/2. However, if they can make a 135mm f/1.8, why can't they make a 100mm lens faster than f/2? Could it be because they think the consumer considers this focal length only good for macro photography, and thus Canon and all the others just keep making new f/2.8 macro lenses in this focal length? Well this consumer wants something different!