Ewww upscaling! Native all the way! (Actually kinda sad we are talking about just 1080p - PC master race indeed).
Oh, certainly there is nothing "official" - just silence from Microsoft. That's why people are talking about sources, rumor, etc. But it's been a few days brewing now and Sony has already come out and clearly said 1080p native on their side already. The silence from Microsoft is rather strange and perhaps telling in and of itself.
When put to the torch and asked directly multiple times, all I can see them saying so far is:
"I've seen COD: Ghosts running on Xbox One. It looks f'n amazing. Wait for real footage, then judge for yourself."
Maybe Microsoft is dealing to throw more money at Activision to get it pushed to 1080p. Or to have it downgraded on the PS4 after the fact.