They are.
Any commercial vehicle that uses a diesel engine in california, and rv coaches using diesels registered in CA are required to comply with the diesel HD I/M bs they’re pimping.
This is not news, it’s been known since january last year. they just finalized the regulations last month, however. They didn’t change much though.
Bad enough i’ve been dumping my diesel trucks while I can and switching to good old ford gassers.
Before diesel engines became more common big trucks ran on LP gas, as did farm equipment.