I don't doubt that they can sell several million, by bundling it with told IP sequels, like Halo, and Fable. They can easily sell 10-20 million in a year.
But by doing this, they don't actually profit from it. xbox fans will buy a more expensive set-up, Microsoft will lose money (I can't see them selling that thing for profit), gaming will require more peripherals, the market will be more divided.
"Nice job breaking it, hero."