I'll answer policy-side questions (or at least go back to the listmod team and get you an answer to those questions). I don't have all the technological understanding to answer coding questions, but I can try to answer to the best of my ability. Here are a few FAQs:
It is allowed only if Xalxe allows it, which he will do on a case-by-case basis. Contact him.
One large concern we have with these private topics being within MS is that those with scum threads may accidentally post in the game thread causing irreparable harm to the game. To solve this, chamber has given Private Topics a different appearance.
It's functional. I wouldn't be surprised if we get one implemented that isn't quite so ugly in the future, but that's not something I have much familiarity with.