I could see them adding it to the MacBook, especially if they make the entire trackpad surface Touch-ID capable. Macs are higher-end, higher margin products. Implementing something like that on a mouse would require doing the same thing across the whole surface (or else it gets too complicated/clunky), which I think at this point would be prohibitively expensive, unless Apple has come up with some magical solution. Aren't the trackpads already covered in glass? Just upgrade that with a sapphire coating.
This would, of course, be a test and precursor to doing the same on the iPhone, probably in the iPhone 7. Make the whole surface touch ID compatible, and then just put your finger on the screen anywhere to unlock. Or even if it's just the part along the bottom where the "Swipe to unlock" would have been. Then with force touch we can finally move away from having any buttons on the front of the device, enabling tiny bezels and smaller devices. Sure, it's less obvious, but it will happen eventually. And Apple will make it more obvious somehow with software and hardware design.