Very interested as well. I own a 2008 Subaru Legacy GT, which has the exact same engine as the STi except with a different turbo (and obviously engine management).
The 2.5 liter Subaru engine is capable of safely putting down 350awhp without modification to any internals and with a mildly upgraded turbo , as long as it's got plenty of fuel and is running a solid tune. The only real soft-spots internally-speaking are the pistons & piston rings, which seem not to like detonation as much as perhaps some forged pistons would
In stock format, with an opened up exhaust and conservative tune, 280-300whp is easily accomplished with no other modifications.
At the same time, expect peak torque (of about 300+ lb/ft) to be delivered by 3000rpms and power to stay on until 5500-6000 rpms.
I think Porsche purists would miss the buttery smoothness of the flat six engine and how it never gets out of sorts, even at very low rpms in higher gears, but otherwise the engine is a great replacement if someone can make it work.
I'm not worried about the intercooler...plenty of ways to make that work....but I'm curious about the transmission adapter, starter mounting, and electronics.
Also, I think the boxster 5-speed's gearing is actually ideal for this engine. The taller gearing means the turbo will get a higher load, which means earlier spool while giving some nice long-pulling times. Combine that with the drop of ~300-400 pounds + 2 less wheels to drive, and I think the engine will drive like a dream.
Good luck to you. This is one swap that's been waiting to happen.