To say that aviation development and market uptake moves glacially is an insult to glaciers everywhere, or at least the piles of dirty snow that pass for glaciers in a world where average summer temperatures make Venus look temperate. I can develop a fairly long list, but let's consider diesel engines for the moment.
This is a companion discussion topic for the original entry at https://www.avweb.com/ownership/airventure-the-diesel-dance