Issue with current models, I'd be worried about potential mismatch on sizing, track width and wheelbase are different between the GP impreza and the new GP WRX.
However I do know that the Forester and Impreza utilize essentially the same base chassis, their wheelbase, and track width are exactly the same, much like the relation of the Legacy to the Outback. I'd imagine their more closely related than the current WRX is to the current Impreza.