I think people should be able to delete threads, usually the people make a map submission that they later don't want or deleted the video in the thread. I have wanted to delete threads and i know other people have too! Maybe just have a little delete thread button at the top left/right that when you click it, it would say "Are you sure you want to delete this thread?" Then you can press Yes or No or Accept or Cancel or something along those lines.
No support, they could delete something that they broke a rule or anything (I know mods can see deleted threads)
The Moderators would still have to go find the thread to archive it. Just report your post and request for your thread(s) to be locked/archived.
No support, you can just do what @Alex said. Plus, if you made a mistake or put something that you didn't want in there, just edit it