I understand what you mean...
However, if you think about it, on what occasions do you stumble across older content that brings you value today?
For me, the straightforward answer is through a Search engine. I often google things like: "Best in-ear headphones Reddit"
I guess the questions are:
  1. Is the right place to solve this problem here on SN?
  2. And what additional value, if any, would a feature like this have for users? Would it also have negative incentives / implications? (Reddit is probably the best case to study)