Going the way of the turbocharged engine makes the most sense if you wanted to make serious horsepower. The Cosworth powered engine would have more similarities with the Cosworth tuned Subaru WRX STI or the Litchfield Type 25 WRX STI both UK market Subaru WRX STIs. The Cosworth lump will produce in excess of 330bhp coupled with some specific bolt on parts in order to fit the Subaru BRZ. Note that the lower bonnet-line would also mean a front mounted intercooler compared to the top mounted one in the WRX STI. Other details of the build include an HKS derived turbocharger, a Cosworth billet crankshaft (obviously) and a limited slip differential to rein in the extra horses and torque.
External modifications seems to be limited to ride height correction due to plonking in a set of KW adjustable suspension system with Whiteline anti-roll bars and a set of 18inch wheel and Advan tyre combo.
I also don't find it that surprising that an Australian company has decided to come up with a tuning package for the Subaru BRZ. Reason being that Subarus are pretty popular over there.