Nikon and Canon claim that in-lens image stabilisation is superior.
There seems to be something to these claims, but it also seems like a very minor advantage. And the disadvantage of having to buy IS over and over again in each lens, is a very clear disadvantage.
Both Nikon and Canon have in-body VR/IS in their compact cameras.
Obviously, with a fixed-lens camera, the distinction between in-lens and in-body IS disappears.
But the fact that their compact cameras have IS, shows that they too acknowledge that image stabilisation is valuable.
But Nikon and Canon (and their customers) have so much invested in separate VR/IS lenses, I really can't see them releasing a camera that has image stabilization in the body.
Maybe they'll surprise me.