Most of the manufacturers already have made updates to their motors to comply with the new standards.
No catalytic converters but a bunch of emissions hardware on the motor. From what I hear there was a slight HP lose so to combat that the motor uses a little more fuel to keep the HP rating. Makes alot of sense, cleaner air from the trucks but more refining emissions to supply more fuel for the cleaner burning motors.
I know my Mercedes MBE926 is compliant and that was the main reason it took 3 plus weeks to change out a stinking head gasket. They can't get parts for the new emissions equipment.
2012 Showhauler 28'6" Motorhome on a Columbia w/ 450 Mercedes.