The automaker has said it will offer gasoline, diesel, 48-volt mild-hybrid, and plug-in hybrid versions of the inline-6 powertrain. The orange high-voltage cabling attached to the middle engine in the photo indicates it's one of the hybrid versions. Expect most if not all versions of the engine to be turbocharged.
The gasoline version will use Mazda's Skactiv-X technology, which uses sparkless ignition (like a diesel) to light a rich mixture of air and fuel, which then compresses a lean mixture for the rest of the cylinder (a spark plug is also included for use under certain conditions). The goal is to achieve diesel-like fuel economy without the high levels of nitrogen-oxide emissions.
2021 Mazda 6 Carbon Edition
The engine is expected to be paired with an 8-speed automatic transmission, and will be mounted longitudinally. That seems to indicate rear-wheel drive, as longitudinal engine positioning wouldn't make much sense with front-wheel drive. Mazda has only discussed all-wheel drive so far, though.
Mazda hasn't discussed any potential applications for the inline-6, but one theory is that the new engine will be used in the next-generation Mazda 6 sedan, which is expected to appear toward the end of 2022. It's unlikely that Mazda would develop a new engine and platform for just one model, so some of the automaker's other vehicles could potentially get the inline-6 as they are redesigned in the coming years.
Mazda's lineup is undergoing a transformation as the automaker tries to move upscale. That means no more MazdaSpeed models for the time being, but Mazda has said it will still focus on engaging driving dynamics.