I'm not sure about the 650D/T4i -it may appear soon, but my guess is that Canon feel that they really need a new sensor to distinguish it from its two predecessors. Without a new sensor, they'd have to upgrade key specifications to differentiate the 650D, such as the autofocus system (e.g. 9 pt all cross type), viewfinder (pentaprism), shooting speed (6 fps) or control interface (second command dial). I doubt that one of these features on it's own would tempt people to pay extra over the 600D price and too many would mean it steps on the XXD line's toes. Therefore, I think that the 650D will need a new sensor to be a viable proposition. I don't see Canon launching its new APS-C sensor on a "Rebel" body, so I think that anyone waiting for this replacement will have to wait for a 7D MkII announcement (autumn?).