The devs could make a forum section called the Thread Graveyard or something along the lines of that, where all the locked threads are kept. Any thread that is locked automatically goes to the Graveyard.
Sounds unnecessary. First, the Rules needs to stay (it's locked), and second, even though threads are locked, they can still be relevant to the forum they're in. As other threads get posted in, the locked thread falls down, eventually to page 2 of the forum, found only by the adventurous and people searching for it.
I think if the devs have useless closed threads that they would just delete them instead of placing it in a ''thread graveyard'' anyway.