On that point, I could see the lower tier fuel engines having a manual throttle in the GUI. I would also make the turbine require them, since I doubt you would ever hand throttle a turbine.
You are are correct on the diesels, but I didn't mention them since we have gone green in RC and only used Ethanol based fuels that are renewable. LOL. Oh wait just hit me....new idea for another RC fuel and engine combo. Bio diesel. Would need a refinery type machine. Engines would be high torque, low RPM like real diesels. Might fit in the huge gap between gas engines and turbines.