We didn't know about this restriction back then. But yeah, that restriction effectively eliminates the possibility of a non-Professor like Sirius being Hat & Cloak.
Yeah. Which, as the example of Skeeter teaches us, means that we could look for a weaker link in the chain: the professors themselves. Imperius/Obliviation strategies have been discussed in the past, but Polyjuice Potion hasn't. Would that work? Dunno. Moody fooled the wards in canon, but that was probably because the fake was the only one to ever get keyed in as a Professor in the first place. Would Polyjuice let Flitwick or one of the others be replaced?
Update: Discussion has moved on to a new thread.
The hiatus is over with today's publication of chapter 73, and the previous thread is approaching the 500-comment threshold, so let's start a new Harry Potter and the Methods of Rationality discussion thread. This is the place to discuss Eliezer Yudkowsky's Harry Potter fanfic and anything related to it.
The first 5 discussion threads are on the main page under the harry_potter tag. Threads 6 and on (including this one) are in the discussion section using its separate tag system. Also: one, two, three, four, five, six, seven. The fanfiction.net author page is the central location for information about updates and links to HPMOR-related goodies, and AdeleneDawner has kept an archive of Author's Notes.
As a reminder, it's often useful to start your comment by indicating which chapter you are commenting on.
Spoiler Warning: this thread is full of spoilers. With few exceptions, spoilers for MOR and canon are fair game to post, without warning or rot13. More specifically: