I doubt it's official word from Subaru. The dealer certainly didn't tell my mom to change the oil in her 2013 Legacy at 3,000 miles, and that has the FB25 timing chain motor which is supposedly harder on oil during break-in, and originally did carry a 3,750 mi factory fill OCI recommendation. Subaru explicitly extended the factory fill OCI in the FB25 to 7,500 mi in 2012.
If it's not in the FSM (or an addendum) it's not officially from Subaru, I don't care what the dealer says. I've had my dealer tell me that exchanging the brake fluid every couple of years is not necessary, and that all they do when a customer asks is bleed a little out of the calipers. This same dealer insisted that a 2011 Outback with the EJ25 should be getting 5w20 synthetic oil, which Subaru doesn't recommend for any engine.
With how thin the factory oil is, I can certainly understand wanting to drain it, but you're draining away a bunch of beneficial additives. The question is how long can you stand to own it without doing any sustained hard driving. As long as the oil stays cool, even 7.9 cSt will be fine, and I'll bet by 4,000 mi the oil is actually getting thicker.
Leaving the factory fill in for a full OCI is not as scary as you might think. I'd be much more worried about TBN than wear metals. Go over to BITOG and have a look at the factory fill from my Civic which went 6k mi. Wear metals went up in the second OCI. The assembly lube and surface coatings are there doing good things. We'll see how my mom's FB25 factory fill does with a UOA here in a few months. Now if she'd just drive it a bit more...