Not really sure why everyone's so confused about this procedure, it's a common one in the Mazda RX-8 world where an engine is replaced under warranty, and the manufacturer wants as much debris flushed out of the oil and oil cooler system as possible.
So, pretty much, Subaru wants an oil flush performed at the very first 6k mile service, or anytime the engine is opened up, and parts repaired/replaced.
There have been recent issues with Subaru motors being built with too much sealant used at the factory, so this is a way for them to try to flush some of that out of the engine before it gets stuck in the oil pickup screen.
Nothing really to see here, aside from the oddly sized oil filter gasket that can leave a big gap between the oil filter housing, and the oil filter itself.