I just had an interesting conversation with some fellow instructors at other institutions about the pedagogical value (or demerits) of allowing students to retake quizzes, either multiple times or indefinitely, and we came up with a solution that we all wanted but nobody's LMS would do: random draw with no repeats.
The idea is that one could build a question bank, for example, containing 100 questions. Students would get a quiz that drew 10 of those questions. If they were not satisfied with their score, they could take a second attempt, but it would draw 10 different questions; they would not get any of the same questions they had on the first try (so no just memorizing!). They would be able to take this quiz up to 10 times, until they ran out of new questions. Ideally, this would be paired with a "keep latest score," so that each successive attempt would replace the previous score, thus motivating students to study what they missed and do better on the next attempt, rather than just retaking and hoping to get "lucky" with a new "best of 10."