Clicking on the all-wheel-drive link reveals that it has the exact same safety ratings and features listed as the front-wheel-drive model. Both pages also have links to the same technical data sheets, all of which are for the 2016 Mazda6. This is the case with the 2017 model listed on the NHTSA site, too.
Naturally, this by no means confirms that Mazda is bringing an all-wheel-drive version to the United States. It's possible the inclusion was a mistake, or someone might have even typed an "A" instead of an "F" when creating that page. But also considering Mazda's interest in offering all-wheel drive, the existance of all-wheel-drive Mazda6 variants overseas, and the likely minor technical hurdles to overcome, we'd say the odds are pretty solid that we'll see four driven wheels in a Mazda6 in the near future, even if not this model year.