I like the contains idea, it allows the writers and readers to independently and individually decide what's a bug and what's a feature.

So, should we consider Contains: and Does Not Contain: as header items and have the likely suspects for those two lists as available tags, thereby providing guidance for the posters when they write their headers?

One thing spnroundtable does well, in a fandom specific way, is have themed rec posts where commentors are encouraged to add their own. They also have discussion posts on meta themes that are sometimes very popular and full of interesting comments. By having someone get the ball rolling with the original post, you get more response than just saying you allow recs or meta posts.