It looks very much like an American-spec Mazda6 to our eyes ... except for the strange, possibly temporary exhaust outlets, which might be required for EPA testing. The rear looks like a current-look car, rather than the revised 2018 styling that will get the 2.5-liter turbocharged gas engine. Since the Mazda6 was originally supposed to get the Skyactiv-D engine, we can only assume that if it's at an EPA facility, Mazda is hoping to bring it to market here – likely sometime after the CX-5 goes on sale.
If Mazda can get approval, it'll be another point of differentiation between the Mazda6 and its competitors – there's no currently-approved diesel sedan that's a direct match. The smaller Cruze and larger, more expensive offerings from BMW and Jaguar are about it.
The fuel economy guide (PDF) produced by the EPA back in late 2017 lists both the CX-5 and the Mazda6 as having diesel engines, but neither are rated, and as we know at this point, neither are on sale or have an official timeline for doing so. We can assume anything with an application in progress made it on the list, whether approval would be granted or not.
It seems unlikely at this point that Mazda would abandon the Skyactiv-D in America. It's a solid part of their strategy, although a product roadmap released a few months ago shows that Mazda expects diesel sales globally to taper off after 2020, to be supplanted by plug-in gas hybrid, EV, and fuel cell vehicles. But between now and about 2030, pure diesel cars are expected to be a small but significant portion of Mazda's product mix.
We hope this means we'll see the CX-5 emerge from the approval process and hit dealer lots soon, to be followed by the 6. If we hear anything else, we'll keep you posted.