That quote from Moffat is the only thing that goes against it, really. But Moffat also said there would be no classic enemies this season, yet we have Cybermen in the preview for the next episode. We know the Doctor lies. Maybe Moffat lies too. Or maybe it's just a white lie because he sees the ganger as real, as you say.

Here's how I just wrote it all up to sum it for myself and post it on another forum:

This is why the Doctor showed up wearing a different coat at the start of Let's Kill Hitler. This is why he didn't want River to give him her regenerations, but she did anyway. This is why he suddenly likes apples, when before he hated them. Also, he solved a Rubik's Cube puzzle in this latest episode, but in Night Terrors (which was originally meant to air in the first half of the season, when it was the real Doctor) he said he hated Rubik's Cubes.

If the Doctor at the start of The Impossible Astronaut was really 200 years older, then I think that was the ganger too. He doesn't look any older. We've seen that River aged from a child to an adult as Mels. The original first Doctor aged into an old man. The Master aged the tenth Doctor. So we know that Time Lords age even if they don't die from it. But 200 years and he looks exactly the same. If he were a ganger, he might not age because he's made of Flesh. He also appeared to be faking some of his knowledge with River.

When the Doctor was shot by the astronaut, the ganger began to regenerate. Normally he wouldn't be able to regenerate because he's not a real Time Lord, but remember -- River gave him her regenerations in Let's Kill Hitler.

I think this is the best overall idea we've come up with yet. Much better than alternate-universe-Doctors. Go teamwork!

~is now imagining a scene from the finale when the bad guys realize that there are two Doctors, their plans are foiled, the music starts up, and both Doctors rock back on their heels together, saying "Ha-haaaa, yeah" and pointing appreciatively at each other at the same time~