I hesitate to enter this discussion as the moderators have broadly argued against this suggestion.
However, I believe that the OP was motivated by a wish to help the moderators, so that the moderators did not need to keep an eye out for zombie threads being resurrected years after they were last updated. And I agree with his suggestion.
Technical aspects
I did some quick research online, as I am sure that other forums (discussing any topic under the sun) have pretty much the same issue. I believe that these forums are run on the PhpBB platform and found these threads online that contain some modifiable code that the admins can use.
https://www.phpbb.com/community/viewtop ... 1&start=15
https://www.phpbb.com/community/viewtop ... #p10895205
Moderating aspects
I take onboard
CR001's and
Casa's arguments about OPs wishing to update their old threads after a long time with the status of their legal cases or long running appeals.
But anecdotally, I would say that 8 out of 10 cases that are added to after 6 months to a year are by a person other than the OP, who has a similar (sometimes very tenuously so) case to the OP. In most such cases, the moderators have had to detach that post to a new thread.
I suggest that the system work in reverse. All threads should lock automatically after six months of the
last post (so it is important to understand the code updates suggested above). There can be a link/button there for the OP to request the moderators to unlock the thread or they can post the request to unlock the thread in the "Comments about discussion boards" forum, as they currently do to change the username or delete accounts.
That way, people can still view old threads without accidentally reviving them.
Related suggestion
On that point, I also suggest that threads older than two years in the UK Immigration forums (both Tier and non-Tier) carry a health warning that the law has likely changed since then and to post a new thread confirming the law rather than assuming that it has remained the same. This would be particularly useful for people who find the forums off an external search engine.
I am not a lawyer or immigration advisor. My statements/comments do not constitute legal advice. E&OE. Please do not PM me for advice.