Indeed, and Canon just wouldn't put a sensor into the 650d that can outgun the more expensive aps-c bodies. That's why they called it "650d", there will be a 70d with a sensor upgrade and *then* they'll put into a "700d".Why not... think of the 450D (12 MP), which outgunned the 40D (12 MP). After the 450D, the 50D got a new 15 MP sensor. There is no reason why the 650D shouldn't get a new sensor, which will be later outperformed by the sensor of the 7D2.
I'm sure you meant 40D=10, and I like you're reasoning -- whether or not Canon does is another matter, to be sure
Surely, the 650D sensor will give us the first clue as to what is actually going on in 1.6x land. If there is no new sensor, then its clear that they are sqeezing out whatever additional blood is left in that turnip, and 7D2/XXD should get new ones. 7D was, after all, the first to get the18mp sensor, which subsequently appeared in the 550D and then the 60D. If you review the history, you find there is no rhyme nor reason to which sensors appear in which product lines first. Well -- except that Canon wants to get a lot of life out of the 18MP
I note that the Rebel has already been through two cycles with the same sensor (both 550 and 600), so to me it would be unusual to see a third Rebel refresh with the same sensor -- especially since the Rebels were the last to get this one anyway, and since it is already 3 years old. I get that the Tsunami set things back a ways, but 3 years is a long time especially in Rebel land.
Moreover, it would not be unusual for a new sensor to appear in the Rebel first without first seeing XXD time: the 10.1MP sensor of the 40D first appeared in the 400D. So in that sense, the Rebels can be seen seen as a proving ground for new sensors.
Conversely, it would not be unusual for a new sensor to appear only in the Rebels -- Witness the 450D, at 12MP which was never seen in the xxD line -- XXD went from 8 (30D) to 10 (40D) to 15 (50D). This was a period of time when the MP wars were very hot: The 12MP sensor didn't last very long even in the Rebels, as the the 450D was replaced with the 15MP sensor of the 500D and subequently the 18MP appeared in the 550D
So to me the rapid pace of the MP wars explains a lot that was happening prior to the Tsunami. Post-Tsunami, we ma have some technology maturity and we have recovery from the Tsunami, which is only 14 months old. Sony has certainly signaled their intentions, and Canon will have to follow suit with somethign that grabs attention -- I'd venture to suggest a new APS-C sensor in the Rebel 650D, and because Rebel land is a MP war zone, I think they will bump things up, if only slightly, and even with little or no improvement in ISO/DR beyond software.
of course, this opinion is worth what you paid to read it, and we'll have to wait and see