I don't think the system is advanced enough for me to trust it to make all the right moves I want, even if the 5DIII did have it I'm not sure that I'd use it. The cinema industry has been using manual focus since it's inception, most people are used to it. But I'd hate to have to manual focus that 40mm with that tiny focus ring.
Most ordinary people use point and shoot cameras or camcorders, both of which do autofocus during video. I haven't seen too many people using a DSLR to take sports videos either, manual focus is fine for cinema productions where you rehearse a scene over and over, and the focus puller notes the lens focus positions as each actor moves to their mark on the stage. The method has been used almost since the first movies, and it works - for cinema, that is.
The issue comes when a non cinema photographer wants to take a live video of their kids playing, or a soccer game,, or any situation where there is rapid random movement, and expect to use a DSLR like the 5D MK III.
The T4i is the first Canon DSLR to do this, but expect it to happen to all of them if its successful. It might not be the best solution for cinema, but for ordinary video of kids and sports, it really is going to help.