For example, what would be inappropriately off topic to post to LessWrong discussion about?
I couldn't find an answer in the FAQ. (Perhaps it'd be worth adding one.) The closest I could find was this:
What is Less Wrong?
Less Wrong is an online community for discussion of rationality. Topics of interest include decision theory, philosophy, self-improvement, cognitive science, psychology, artificial intelligence, game theory, metamathematics, logic, evolutionary psychology, economics, and the far future.
However "rationality" can be interpreted broadly enough that rational discussion of anything would count, and my experience reading LW is compatible with this interpretation being applied by posters. Indeed my experience seems to suggest that practically everything is on topic; political discussion of certain sorts is frowned upon, but not due to being off topic. People often post about things far removed from the topics of interest. And some of these topics are very broad: it seems that a lot of material about self-improvement is acceptable, for instance.
I have this heuristic which states, if a bunch of smart people get excited about something, you should check it out. There's no obligation to also get excited about it (a lot of smart people get excited over classical literature, which does less than nothing for me, but I'm sure this is a product of my draw in the lottery of fascinations and not sloth.)
At this point, "anything that you find interesting and doesn't get downvoted into oblivion because nobody else finds it interesting" seems a reasonable criteria for "appropriate for LW". There's a chance that this allows a spontaneous influx of people who want to write about classical literature or social justice politics, but as long as our core material is The Sequences and the wobsite has MIRI, CFAR, and Future for Humanity Institute in the upper right, I'm not worried about losing what makes LessWrong shiny.
Beware. That's exactly how people show up for every horrible Transformers movie in enough numbers to fund the next one.