This seems like unnecessary fragmentation. Reddit became huge because it gave people interested in a topic a one-stop place to discuss their topic. Putting the interested people together gave a network effect that attracted even more participants.

Creating new discussion venues (subreddits, usenet groups) is generally only worthwhile if an existing venue gets too crowded or cluttered to discuss a niche topic, or the niche topic becomes big enough that the existing venue is happier if the niche splits off. Example: there is a general programming forum, Rust gets invented and people talk about it there, then Rust becomes a big enough topic that a Rust forum is warranted.

I'm a not-even-newbie to Rust but I'd be happier if the lemmy.ml and lemmyrs.org Rust forums somehow got merged. Because of federation, I'm basically indifferent to which Lemmy instance actually hosts it.