I really dont want to discuss why i want it, as i know its a hot topic, but ill say this.
I like to use Auto ISO a lot. I also sometimes feel the need to switch to Manual mode as i want a certain DOF and a certain shutter speed. I also find i use +/- EC quite a bit in the other modes. Having a bit more control over the exposure when the camera is setting the ISO seems like a good idea.
Seeing as only Evaluative metering takes its reading from the selected AF point and locks it when you half press the shutter using the other metering modes sometimes gives the wrong result, especially if im focusing and recomposing.
Its not for everyone of course, and its not something id' use a lot, but the fact that Canon have implemented it on the 1DX seems to indicate im not alone.