Scrolling through there are so many posts with repeated replies, and some other posts which are giving wrong information (which was accurate atvthe time it was posted)
And mostly more recent posts with litle replies go to the bottom of our feed.
Should there be an expiry date for posts, after which the are locked or archived?
I think you are worrying about the issue that when someone reading a thread and founded that information was outdated. So you are thinking, there should be a system to implement to delete/locked/archived the outdated posts. But the problem is we can't say the superseded data/information was not worthy or to be locked/deleted since those information/data also needed when we analysing how things have been changed with the time. We can't just locked/delete history.
This is the famous quote of "Thomas Alva Edison" when someone asked what is the reason for trying again for inventing the light bulb since you have failed 10,000 times.
"I have never failed, I've just found 10,000 ways that didn't work"
I think that quote will give you the answer for what you have been looking for. That outdated information, replies and answers given by other members should be readily available when reading a thread. Then only we can say those information/data has been outdated or superseded by the newest with reference to the older ones. The best example for this kind of thread is
Wall Observer BTC/USD - Bitcoin price movement tracking & discussion. Imagine what would happen if this thread has an expiry date or if we implement a system to delete/archived/locked the thread or even outdated posts? Then we couldn't be knowing about the history of bitcoin price movement and most importantly bitcointalk users behaviour when bitcoin crashed and even bounce back, price speculations with the time, etc...
But, also users don't lock their own thread now.
That is a critical issue that should be addressed by staff or mods. I also found out most of the members hesitate to lock the thread even they got their answers for what they are looking for. Instead, they are allowing those so-called spammers or shitposters to spam fest with their thread. So as responsible members we should lock our threads when we got the answers.