“With diesel engines, all the problems with fuel availability goes away”
From a strictly UK perspective the reverse is true. The problem with diesel engines in aviation is that most will not run on diesel, but use Jet A1. Most small airfields and strips are near a filling station and it is 95% likely you can get Mogas as it is the fuel used by almost all micros and quite a bit of light GA. Very very few will have Jet A1.
The Rotax has been certified for years and will have logged lots of time IFR. The new bread of 4 seaters using the 912 will be much cheaper to run than the old American machines (P400 MCR4s). The next gen home built 2 seaters which are on the drawing boards will give 90kn on 50 hp using industrial engines (mogas or Avgas), with similar lifting power to a Jodel.
Rod1