> I also noticed that in recent years many subreddits have increasingly been taken over by memes and other low quality posts and so users looking for more substantial content have already moved elsewhere.

I feel like I've seen the opposite, generally- there was always kind of a tension between serious posts and memes, but in the past few years it seems to have become much more common to see subreddits with a counterpart strictly for memes (/r/chess and /r/anarchychess being a recently popular example).