One challenge not discussed here is when an accepted and highly voted answer _used_ to be a good answer, but no longer is in later versions of whatever software/platform/library is discussed. This is also something that gets worse over time, like the uniqueness problem. I think it's worse than the uniqueness problem, multiple duplicate _good_ questions/answers don't actually harm, misguide, or delay anyone looking fo…
Quora has recently introduced secondary voting mechanisms where answers will randomly have a "is it still relevant" toggle for users to continue providing signal beyond the initial vote.