From the welcome post:
Examples of subjects that are off-topic (and which moderators might close down) include [...] anything that cannot (yet) be usefully formalized or modeled mathematically.
This seems open to an undesirable interpretation (discussion of how to formulate things that haven't yet been formulated and exercises in working through pre-formal examples, in an attempt to isolate principles that can then be explored more systematically). It might also encourage cargo cult formalization.
I've edited it to the following:
...But the list does help us to point out what we consider to be on-topic in this forum. Besides the topics mentioned there, other relevant subjects include groundwork for self-modifying agents, abstract properties of goal systems, tractable theoretical or computational models of the topics above, and anything else that is directly connected to MIRI’s research mission.
It’s important for us to keep the forum focused, though; there are other good places to talk about subjects that are more indirectly related to MIRI’s research
Today, the Machine Intelligence Research Institute is launching a new forum for research discussion: the Intelligent Agent Foundations Forum! It's already been seeded with a bunch of new work on MIRI topics from the last few months.
We've covered most of the (what, why, how) subjects on the forum's new welcome post and the How to Contribute page, but this post is an easy place to comment if you have further questions (or if, maths forbid, there are technical issues with the forum instead of on it).
But before that, go ahead and check it out!
(Major thanks to Benja Fallenstein, Alice Monday, and Elliott Jin for their work on the forum code, and to all the contributors so far!)
EDIT 3/22: Jessica Taylor, Benja Fallenstein, and I wrote forum digest posts summarizing and linking to recent work (on the IAFF and elsewhere) on reflective oracle machines, on corrigibility, utility indifference, and related control ideas, and on updateless decision theory and the logic of provability, respectively! These are pretty excellent resources for reading up on those topics, in my biased opinion.