Considering how nice the kits are that FFR builds, this one will be awesome. I think there will be a lot of flexability for us Subaru guys. I see no reason that you couldn't use almost any turbo drivetrain, although the kit will probably be designed specifically to use the suspension and brake parts from an Impreza. They may also build it to use some of the interior pieces as well.
As for competing with the Smyth car, that car is specifically being build to be a green car. That car requires you to use the frame from the VW. The FFR will use a custom tube frame, like all their other kits.