So...there's only one example of Canon having "led" with sensors in the xxxD rebel and propgating them to the xxD - the 10 MP sensor, but three examples of a sensor debut in the xxD line (prior to the 7D release).
You are looking at this the wrong way, IMO .
The historical pattern is not that new 1.6x sensors first get introduced in the xxD line.
The pattern here is that once a new sensor generation comes along, it gets reused in both the Rebels and the xxD line.
The only exception is the 12mp sensor in the 450D but that was because the 50D jumped straight to 15mp - rather than reusing the 12mp sensor.
I'd love to be proven wrong but it looks like the 650D sensor is Canon's 'new' sensor.
So, it's very likely that this 'new' sensor will be reused in the 70D as well.