I think its a new sensor because the pixel masking necessary for phase-detect pixels has to be added underneath the microlensing, as the microlens is an important factor in making FPPD-AF work. That would require some degree of reengineering...even if it is relatively minor. There may also be additional activate/read wiring to read out only the phase-detect pixels for AF before activating the full sensor for an image readout.
Well, the sensor surely had to be tweaked to accommodate the hybrid AF and maybe other minor enhancements.
You surely cannot just plug-in a 7D sensor in the 650D and expect it to have hybrid AF.
But the underlying sensor architecture and technology appear to be the same.
Hence, the sensor will perform the same way (more or less) as the 600D/60D/7D sensors.
Or, as I put it in another post:
It's a brand new sensor ... with the same performance as the old one .