Design a better comment tree navigation system. On the sly, sneak it in as an inobvious option that has obvious benefits and let the awe flow from there. Nobody has solved comment tree yet, why not be the first? Incidentally, your keyboard shortcuts don't work well for me and are not re-configurable (outwith greasemonkey). Make it easy to skip the dross, please.
There's moderation, tricksy stuff like redundant et al, but then there's "get this shit off of here". We should all have a downvote option that triggers deletion above a certain threshold of non-AC users. Some shit is obviously crap and if enough of us think so, then you should trust us and delete it. I should be able to browse fairly safely at 0.
SD has remained always in my top 5 new sites, for well over 10 years. Almost all good tech stories are here, and the comment threads can be of the highest interest, with many spin offs and detours to visit interesting links or research interesting concepts. The register has better tech content but the commentary is single-child nested which stifles proper BTL discussion. Slash is all about BTL. Just keep the stories focused and let the conversation flow.