I think part of the reason we don't see new designs is they wouldn't be that much better. Often a technology advances rapidly, then hits a plateau where future

I think part of the reason we don't see new designs is they wouldn't be that much better. Often a technology advances rapidly, then hits a plateau where future improvements are just modest. Think of jet planes, where everything since the 707 has just been a modification. That is why 50's and 60's planes like the b-52 and the a-10 are still flying. Or space rockets, where we are still just duplicating performance from the 60's (but with SpaceX we finally have something new). Piston planes advanced very rapidly starting with the Wright brothers, but then hit the plateau in the 50's, and the next step up, jets, is just too expensive for most private pilots. Yes, it is possible to produce better small piston planes, but the sales are too small to justify the needed investment. Maybe electric planes will finally get us something new and better.