"The one thing that this set-up does not let you do is change a question to have an answer that used to be marked wrong now be considered correct, and then re-grade the quiz. That is a useful feature in Moodle (at least for non-adaptive quizzes), and one we would need to retain."
However this does not apply well to every question types.
For short answer or numerical question types, if you change the answers or the grading value, you just change the resulting grade.
For multiple choice or match if you change the answers, you change the question display. Should we continue to allow teachers to change those question types or just offer the save as a new question if the answers text has been modified?
P.S. I am planning an improved multianswer (cloze) editing interface that will enligthen the diffs between the stored question and the modifications done .