>>>/lp/ - Let's Play!
Still small, but I think it has a potential to grow. There's plenty of people who enjoy LP content, and there's plenty of good LP content that isn't aimed at a young audience. Most importantly, it already has a userbase, it's just slow. It also has a few content creators, from amateurs to content creators with a small following, and plenty of people who know what kind of advice to give new LP creators.
It uses a liberal definition of "let's play", and doesn't only include traditional "let's plays", but encourages all kinds of stuff like speedrunning, commentary, streaming, and so on. Basically, if it uses someone's raw gameplay to create content for others, it fits.