Folks, this has nothing to do with reputation. It’s about ranking answers. Please stop trying to close it as a duplicate of one of the decade old discussions about reputation.
I think it would be beneficial if the ranking of very old answers that have already accumulated a lot of votes was more dynamic. There are many ways to implement a more dynamic ranking. One of them would be to have the scores we're using to rank the answers decay either over time or based on some activity measure, so that new votes, which tend to be more informed than old votes1, would have more impact on the ranking.
I'd like to discuss whether allowing answer scores to decay toward zero would be a useful to make that ranking more dynamic, and if so, talk about ideas on how we might go about it without causing larger issues than the ones it could solve. This is not a proposal for a change. Think about it more like brainstorming. Stack Exchange is founded on collaboration, so let's collaborate and entertain some crazy ideas. Maybe the discussion will spawn some ideas that aren't crazy.
Thinking about the discussions around pinning accepted answers and dealing with obsolete answers, I started wondering why twelve year old votes (up or down) on posts stick around forever. I don't have a specific proposal, so this isn't a feature request (I would be surprised if some version of this hasn't already been suggested). I think there has been talk of weighting the score of an answer based on the age of the votes, but I wasn't able to find anything about letting them age away.
It seems to me that if answer scores were more dynamic, it would be easier to solve the outdated answer issue and we wouldn't need to pin an answer to the top of the list to overcome popular-but-wrong answers with insurmountable scores. Allowing votes to decay over time would also mitigate that early votes (and the choice of accepted answer) may be cast with knowledge of only a fraction of all the answers a question might get in its lifetime. If we let answers decay to a zero score, we could also reset certain questions back to "unanswered" if there is no accepted answer and have the community bot bump them for the community to take another look at.
I don't think there should be any changes to anyone's reputation or badges as votes decay; What has been earned should stay earned and I don't see that forcing people to constantly earn reputation to keep their privileges has much benefit compared to offsetting the huge advantages in score old answers have over newer ones.
In my opinion, only the answer scores should need to be freshened up with new votes. Questions don't compete for visibility using score; they can be bumped and bountied for example. I think both downvotes and upvotes should decay. I feel that post activity (views, comments and edits) should affect how fast votes decay, but I can see a lot of tricky bits around that. Maybe whether the user who posted the answer is still active would be a factor to consider when decaying the score? Active users might be more likely to keep their answers updated, so decaying the votes might be less useful?
What do you think? What factors would you use to mitigate the momentum of old answers that have had a lot of views and votes? What factors should speed up or slow down the decay of votes on an answer if we did let votes decay? Would the decay possibly helping users get out from under an answer ban be a good thing or bad thing?
1. Newer votes are more informed because ideally the question would be clarified and improved over time and there would be more answers to look at when deciding whether a particular answer should be upvoted or downvoted.