I can't see them doing that for a 2015 wrx you would need to include a crap more parts to make something like that work. Turbo vs supercharger
A bigger turbo, a J-pipe, an intake and an intercooler. Plus what ever else they think might be necessary to include in there, which I don't think would be too many other things.
Seeing their price point on this supercharger power kit, I don't think it's impossible that we'll see a Cosworth kit for the turbo FA20 down the road. Then again, it could be wishful thinking.