Stuff posted without a catagory would get the PR heading. If its not related its fine under the PR cat. If it becomes related its fine. Commercial spam and cp/snuff are what needs to be filted completely.
Essentially, if there is a definite project to make through discussion on an off-topic thread; then anyone can make a ‘project’ and let the OP be a wiki;
Projects section threads should have an option for making the OP’s a wiki.