qualitys of a zero-coupled design?
I didn't take it as criticism (I even had to look up the word:-). This stuff is interesting isn't it. No you made a good point about the mixing flows and their relationships.
Just think how good things could be if we could get rid of gravity. In my youth I used to imagine flying in a big bubble in orbit. You could draw some nice figures in space. Then I saw the insides of the space station and the concept of a smooth bubble burst pretty bad.
We did work (when I used to work) on some control systems for unstable aircraft. One of them that wasn't too practical used the set of wind tunnel data that was tweaked with flight test data. The system did a look up of where you were, where you wanted to be and figured up how to get there using the data set to work out control deflections. Worked great on a monster computer we had but at the time the memory requirements were impossible for actual use (this was a long time ago). Then we tried to reduce it to curve slopes which kind of missed when the non linear things were happening (most of the time) Then I luckily got transferred.
With the modern electronics and memory it would be possible in a model but like you said it would just add a layer of stuff to go wrong. Plus we are trying to find out who the best pilot is and which is the best airplane.
It would be interesting to make an airplane that had easily changable wings, tails, etc. locations so you could change the configuration at the field. Three horizontal tail and wing positions, vertical tail profile changes, etc. With modern materials it might be kept light enough to give some answers that would be useful.
Too many interesting problems and not enough time. Even being retired I found the hobbies expanded to fill all the extra time.