It seems that the opposed piston engine has some benefits. Double the acceleration away from TDC means less time at high pressure/temp which may reduce NOx emissions. It also means a more adiabatic expansion. Achates has been working on one for some time. They have some contracts and a partnership with Cummins.
The 2-stroke design may have some benefits as well. I installed some kits from Clean Cams Technology Systems in the past. They took the exhaust cam from a 71 series Detroit Diesel, ground most of the lift off of it, and added a turbocharger to restore the airflow. In theory it was the equivalent of in-cylinder EGR. It was certified to US EPA Tier 2 emissions standards on a fully mechanical injected engine which was quite remarkable.
You know they're not serious about taking it into production when you see the open K&N air filter on it.