I didn't really think that was implied at all. The purpose (in my view) was to expand his abilities and broaden his horizons. Knowing your enemy, in order to better to defeat them.
Remember he only drove the Impreza every other day. Fanbase assumptions could turn up being correct that he switches to the FRS. Either way I definitely expect a different vehicle, otherwise 5th stage will just be a repeating story. I just don't expect to see him in a AWD platform.