Anyone know how compatible, and therefore easy it would be to swap the WRX brakes (the ones that have Subaru cast int othe caliper housings) to an '05 Outback w/ 16" wheels? Seems like it would be a nice upgrade, and likely bolt up pretty easily, no?

Fronts bolt right on, but your wheels probably will not clear them. The problem isn't the diameter, the caliper is actually a bit shorter than the 02-05 WRX caliper which uses the same rotor. It's a lot thicker though and hits the inside of the spokes on subaru 16x6.5" wheels. There are however plently of 16 and even 15" wheels that will fit over them, including the 98-01 Impreza 2.5rs 16x7" wheels.

 

For the rear Kartboy sells an adapter bracket. They don't bolt on since the calipers bolt directly to the backing plate which is pressed into the spindle.

 

In fact, any front brakes from any modern subaru (except the svx, 05+ STi rotors, and probably tribeca) will bolt onto any other subaru assuming the wheels clear. For the rears, sliding, subaru 2-pots, and brembo 2-pots all have different methods of attachments, but any sliding rear caliper will work. 00-04 Legacy and 05 LGT rear discs are the biggest bolt-on oem brakes and are not-vented/vented respectively. Both use 11.3" discs and the same size piston.