Just two weekes ago I sent a e-mail to Schweizer asking if they were considering installing a diesel in the 300C. Maybe something like the SMA 230 hp engine.
I received response immediately and they said they were indeed considering diesels but at the time they were not an option due to cost but they were following all advances in the diesel tecnology.
They also said that the SMA diesel, although in the same horsepower category as the HIO360 D1A Lycoming at 225 hp was to heavy to be feasible.