So I have two points to make here.
First: I think it's clear that this question could be rephrased to meet the guidelines for subjective questions. The problem is that it invites opinion (or speculation) over personal experience; other than that I don't think it breaks any of the guidelines. One suggestion I made in the original thread: Solicit personal experiences on what works and what doesn't in running linguistic discussions for laypeople. (Perhaps nobody will have personal experiences about running a linguistics book club, but I'm guessing some of us will have experience with running popular linguistic discussions more generally.)
Second: I suggested in the bad stats thread that we should aim to help people with practical goals if we want to strengthen the user community here. This strikes me as a good example of that: someone has a practical goal that's related to linguistics, they have a question about how to achieve that goal, and we are in a position to give answers. Good answers will be linguistics-related. (It would be fine to exclude non-linguistics-related answers like "Put up an ad on Craigslist!" or "Make sure to serve snacks!")
Anyway, I think it is very much in our best interest to find some way of refining or redirecting questions like these rather than simply downvoting and closing. We want to be a useful resource, and here's a way in which we can be useful (and enlarge our userbase) without breaking any SE guidelines or diluting the purpose of the site.