You might be right, although I don't think it's nearly so certain. Why wouldn't each niche community just become an even greater echo chamber when they are decentralized and don't have to follow the same community guidelines? Seems to me, you'd be looking at a lot of communities like /r/thedonald.
I think the action taken with /r/thedonald contributed more to what you are warning against (echo chambers) [0].
"Community Guidelines" can mean anything or whatever confirms to the CEOs biases.
From the article
"Current CEO (and Reddit co-founder) Steve Huffman stepped in as CEO following Pao's departure. He's had his own tussles with r/The_Donald: in 2016, he admitted to modifying posts from users on r/The_Donald after they repeatedly sent him expletives. "
And
"Others on Twitter have taken issue with Huffman's letter regarding Black Lives Matter as well, with the Twitter account for r/BlackPeopleTwitter quoting Reddit's tweet with an image of a Guardian headline that reads, "Open racism and slurs are fine to post on Reddit, says CEO."
