Pros: Boxer engine, Subaru built, same basic mounting points
Cons: It's a new engine in a new car, costs waaay more money than other options (aftermarket FI, more available engine like LS or EJ).
The piping doesn't work out with the space in the Toyobaru, you would have to replumb the whole thing, might as well do an aftermarket turbo for the amount of work required, the plumbing has already been worked out.
Subaru Direct Injection vs. Toyota D4-S, not sure which ECU you would use not to mention the rest of the harness for all the Toyobaru's systems.
Same block should have the same transmission mounts but that's not guaranteed considering the Forrester is CVT exclusive I believe
Cons #1 & 2 are usually enough to dissuade most. If you want more power swap in a V8 or something cheap, simple, and available. If you want a turbo just go aftermarket bolt on with a tune. Both are immensely cheaper than getting Subaru's FA20T.
http://www.ft86club.com/forums/showthread.php?t=47004
Edit: Can't wait for these threads asking about the WRX's 268 hp motor
