My biggest question would be how much IS improvement the IBIS would bring to an old EF lens like my 200-700 f/2.8 IS. Would it work well together or might it even work against it? I imagine the IS of the lens trying to bring a stable image onto the sensor and then the sensor moves to compensate camera shake. That might only work if the IS of the lens and the IBIS would be somehow coordinated. The thing I care most about when I buy a new camera or lens is the ability to get handheld shots with even less light than before. If my 70-200 could compensate two or three stops more, that would be a huge improvement.