You are like all of us, wishing for mower heaven. You forgot to mention that the ideal mower would have an air-conditioning unit that bathed the operator in a cool breeze on a 30+ day..
Taking one thing at a time, handles that are hard or slow to fold down are a great problem. I use Honda HRU216's because they are so boring and reliable, but they have many faults, including the handles. Victa used to have, maybe still do, cam-like levers at each side that locked the handles in the extended position very quickly. The problem with that is that the plastic cam surface wears and soon you have to tighten the nut. Then after some episodes of tightening, the nut gets loose on the thread, and begins to loosen itself. So you have to tighten it more and more often. Honda's answer is to have big knurled nuts that you tighten directly onto a threaded stud to force the upper and lower handles together. The problem is that it takes a lot of time to release or tighten these nuts each time. (Not to mention that sometimes they work loose, fall unnoticed, get run over and destroyed by the mower.) I eventually worked out a way of securing the mower on the trailer without folding the handles, saving time.
So there's lots of scope for wannabe engineers to improve mower handles.
Another thing that would be nice - if the handlebar was one sided, a single super-strong bar down one side, allowing us to remove/replace the catcher without anything in the road.