People have swapped the 3.6R into various Subaru vehicles already although not many. Outfront Motorsports (used to be Outback) who build sand rails with Subaru engines turbo'd a 3.6R and found the crank to be the weak part of the engine. At around 10PSI of boost the cranks had a tendency to fail. The 3.0R is more sorted, plenty of folks have built turbo Imprezas with them, including Perrin. The wiring is always the nightmare.
Have you seen the powerband on the new FA20 DIT motor Subaru just came out with? Or the Accelerated turbo kit thread?
Definitely a better and likely cheaper option, even if you had to build the bottom end of the FA20 to handle more boost.