I posted my answer there already. I will reproduce it here:
On Ask Ubuntu we have a lot of questions, and especially a lot of answers, which were super relevant and useful to a lot of people at the time they were posted, but which no longer have value in helping folks find out how to do x, because how to do x has changed over time. Many such posts are highly upvoted, jump up on search engines, and if they are answers show at the top of the by-default-vote-ordered pile.
We don't delete such posts, and I don't think we should delete them or even necessarily edit them to update them (often this would involve replacing all of the content, perhaps making it the same as other existing answers to the same question), because they have a social history value and perhaps can be of use to people interested in user experience and various other aspects of software development - who knows? But the mass of obsolete material is only increasing over time and gradually making it harder for visitors and reviewers to find answers that actually give accurate and current information. It's not at all the case that everything old is out-of-date, but enough of our posts are out-of-date that it's an issue.
Recently Monica from the Ubuntu community team gave me the idea of an archive feature. The way I think it could work would be different for questions and answers.
For answers, 5 users could vote to archive an answer, and it would be pushed to the bottom of the page in all views under a notice that the below answers are archived and may not work any more.
For questions, 5 users could vote to archive a question, and a notice would appear at the top of it stating that it is archived and may no longer be relevant, and optionally and preferably, linking to newer questions with current answers on the same topic.