I think the basis for evaluating the quality of a community lies in the discourse and communication. Submissions are a part of that, but the discussion that follows (i.e. comments) is the most important indicator of change. Personally, there seems to be an influx of reddit-style comments (little substance, meme-oriented) this year, but that could be a general evolution of the English language given the heavy influence of the internet.

That said, evaluating change in the number of comments along with comment upvotes vs. sentiment analysis seems like the only logical way to demonstrate any sort of quality meta analysis. I'm not really versed in qualitative research, so here's my ASK HN: is this even possible?