Move to diesel engines across the RV spectrum a fad?

Diesels have greater mpg which makes them appealing to some even when it doesn't actually save money - fuel cost is higher. They're also nicely torquey (although electric motors are even better).

Modern diesels are also very different from the dirty, noisy ones that didn't last long in the 70s. Fuel is cleaner and emission standards are higher now. They're less noisy than they were in the 70s, but still noisier than gas though.