OP is basically pointing out how forums used to run. Generally geared to a theme or topic but includes spaces to discuss other things with like minded people on the same site. I’ve really missed that more and more over the last few years.
The closest Reddit could to is either have adjacent subs or reoccurring automatically generated threads.
There are a few themes. I’m assuming they mean a pure black mode. That’s what I’m hoping for. That and a jump to next parent commitment button.