Well, in my opinion this is the best single action a LW admin could take, because I think the tacit sexism and racism on LW prevents most humans (who are neither white nor male) from taking the teachings of Yudkowsky seriously, and I think that fixing the representation problem would go a long way towards solving that. Once the global majority are able to take LW seriously, it'll spread much faster, and the world will become more rational.

All the other suggestions I saw previously were just ways to split up existing discussion on LW by categories, whereas this will hopefully bring new people and types of discussion to the community.

I also think that this has near-zero costs besides some moderator effort. Parts of the LW community will be irritated by the idea of spaces that exclude them, because they're white men who have never been excluded, but in the long run, those people aren't very valuable to LW, because they serve to alienate people who aren't white men, and most people aren't white men.