Awesome news, was expecting this since a lot of people would in fact be disappointed if they didn't include a headset with a purchase of the Xbox One. Personally, I will be using my current-gen headset that is probably way better than the packaged headset that comes with the Xbox One. The only downside of this is I have to purchase an adapter for it which will most likely cost $60, equivalent to a game.
Via IGN
Most notably, the Xbox One Day One edition will include an Xbox One Chat Headset, reversing the policy Microsoft announced in June. (Note: IGN has confirmed with Microsoft that the Chat Headset will be included in every Xbox One and not just the limited-edition Day One versions of the console)
Via IGN