You raise an interesting point about decay. I have thought about similar systems myself. One flaw in a simple decay rule would be that some technologies are very stable, e.g., C & POSIX API programming. However, other tech is very fast moving like Python, Ruby, Java, C#, C++, Rust, etc. One idea to overcome this flaw, might be to have moderators (who are specialists on the subject matter) provide a per question decay rule. Example: Something like struct layout or pointer manipulation in C or the fopen() POSIX function might never decay. But something like a parsing JSON in any fast moving language might require annual updates. For example, a question about parsing JSON in Java might decay answers over a one year period to encourage people to revist the topic. I would like to hear Jeff Atwood and Joel Spolsky debate this topic with other "Internet points" experts for an hour-long podcast. They might brainstorm some very intersting ideas. I would also love to hear what they think about the "moderator problem". Some of the topics had incredibly toxic moderators who scared away newcomers and women. (Women are much less likely to participate in public software forums where public shaming is common.)