How about giving a temporary ban to the OP of each thread if his thread reaches 50 pages and still he has not locked it. Obviously, the ANN threads in gambling sections and sports discussion threads should be excluded from this rule.
Also, this can be applied to other sections too, including the Bitcoin discussion sections etc.
This is too harsh and it would never be implemented. The decision that a thread has run its course or not is somewhat subjective, so you can't dish out temporary bans because a user didn't lock their thread that's over 50 pages, what about users that are inactive. The forum runs in a very free way for its users, this goes against that.Also, this can be applied to other sections too, including the Bitcoin discussion sections etc.
I don't think there needs to be any rule regarding threads that are over so many pages, just report them to the moderators if you think it has been overrun by spammers and let the moderators decide.