I would just like to add to @lihaoyi excellent points. Its just a fact of life that discussion can never be how the project leaders would like it to be. How much a person gets heard will inevitably reflect the amount of time and energy they are willing to put into debating. Those that are willing to put a lot of time into debate will dominate the discussion.
And I can pretty much you guarantee you that any measures you put in place to hinder their advantage will rebound and have the reverse effect to what was intended. If you limit the discussions to three threads per person, they the really keen protagonist will put three posts in every thread, while the occasional visitor mayl appear for a subject they are interested in be frustrated and annoyed by the 3 post limit and may not bother to come back. If you have two threads per SIP again it will favour those with time and commitment to write everything twice.
If Scala is to grow then the volume of commentary, opinion and debate will inevitably grow as well. And it is the very nature of human discussion that not only do we humans disagree, we disagree about what is being discussed, what ought to be discussed, what should be the limits of discussion, what is relevant and what is orthogonal.
I find meta discussions, separated from the specific sterile. I particularly dislike threads on moderation, which are really about a specific person, people are incidents, where most people are in the know and all talk about the specific matters whole pretending not to and for those who are not in the know, the whole thread makes no sense.
@SethTisue I just want to add that I hope that nothing I say comes across as unappreciative of your efforts and attempts to find innovative solutions. Managing and moderating a programming community is a near impossible task, far harder than most coding problems. I’m very glad that its your job, not mine and am under no illusions that I could do a better one.