Silvaire - I do think the way forward is diesel or turbine. The high cost of Avgas is enough motivation to see that happen.
With regards your statement about Thielart powered UAV's being dogs, please explain why and on what basis you pass that opinion. Grey Warrior was a development of Warrior and later deployments of similar type were regarded as good. The main issue was finding an engine that could cope with a very wide specification fuel in theatre operations