They chose different suspension spring rates last time (which made it more oversteery).
I'm not sure why they want to do much more than that (if those rumours are even true), because up till now both of these cars have had excellent reputations as twins (slight power issue aside).
Just feels very strange for toyota to take that kind of risk (delayed product launch), heck I'm not waiting around for the car if I like the BRZ - I actually have a deposit on both now just in case.