I'm somewhat curious as to what efforts to design a smaller, better fit engine closer to the original form/size with better fuel economy was tried. Combined wi

I'm somewhat curious as to what efforts to design a smaller, better fit engine closer to the original form/size with better fuel economy was tried. Combined with newer materials. It seems like the flight charismatics have changed so much that pilot recertification should have been required anyway. I have worked on eLearning courses for aerospace in the early-mid 00s but have forgotten mostb of what I learned in that domain back then. It was also mostly mechanic/diagnostic interfaces (ECU, etc)