I have a suggestion that might work. Why not create a sub-forum 'Dead Threads' (optional name) within the 'Suggestion Forum'. Then simple set a time limit on those threads in suggestion forum that if after x amount of time (days, month, year etc) nobody have/has posted in that thread, the thread is then automatically moved to 'Dead Threads' forum. I am pretty sure the Admins/Mods have the power to enable this time limit. Also you can then simple lock the 'Dead Threads' forum so no one will create/post new threads/posts in it.
And I am not exactly sure if people can still post in locked forum so if that is possible then you can also create a rule that nobody is allowed to post in those threads within 'Dead Threads' forum.
You can also state that members can contact you (Mods) if they want to have thread/s brought back into the 'Suggestion Forum'. This of course depends on you (Mods) and member/s reasons for wanting said thread/s back.
That way people can still see/read the old threads, and it makes 'Suggestion Forum' much more organized. Also it makes the job much easier for Mods.
