They had an engine that was to be able to be placed into 182 etc but that never really took off ethier.
Diesel: for _ fuel economy,consistent performance, long mechanical life. virtually maintenance-free if fuel/oill filters and oil are serviced properly, fuel cheap and readily available worldwide.
against = usually heavier, noisier, the need for extensive research, refinement and certification, fuel could "wax" at altitude/cold-soak -because it will happily burn it, doesn't mean it should!
The huge cost of research, development and Certification, for the relatively small volumes of piston GA engines, means the economics are very tight.
Anyone remember the Porsche engine? Robin? (Just 2 I know of)
Thielert was beset with problems, despite having an assured sales-volume .
Jabiru hardly has a stellar reputation in the reliability -stakes.
On the other hand, Where Robin (and others) disappeared from the Microlight market,but Rotax continued development, thrived and has expanded. They now have a very real and potent challenge to the Lycosaurus market.
Lycoming and Continental, having recovered their development and tooling-costs decades ago, must be really hurting....the recent directive on aftermarket cylinders gives a hint of this Complacency, poor quality-control and protectionism is not the way to run a sucessful business!
Meeting the customers' needs and expectations, is, however, a fairly fundamental foundation..
Inevitably, due to the shrinking Avgas market, the future choice will be Diesel (OK, CI ) or Mogas continuing with it's limitations.
I forsee a decade or so of stuff with high maintenance and relatively short life (Thielert) until the engineering refinement gives a whole new era of low-maintenance,affordable GA Piston engines.
I have deliberately ignored Electric....that could change at a stroke with the invention of a light,cheap, high energy-density battery....already, solar cells are edging closer to being practical as an airframe surface-cover....but , although massive leaps forward have been made, there's a huge capability -gap to be bridged.
Just idle speculation from a bystander.