It worked for Reddit. There are several forks of the site, but none of them have significantly put a dent in it because the audience is on reddit.com.
Unless Dev adds Mastadon-esque federation, nobody's going to choose a separate instance over the mothership unless they have no choice. For example, stuff that violates the CoC (voat.co) or their needs require them to do significant mods to the site (lesswrong.com) or they specifically want a different audience (news.ycombinator.com or lobste.rs).
The last two are really funny, since they truly prove that it doesn't matter if you open source your codebase or not. It's not that hard to code up a clone of Dev or Reddit.
note: You'll notice that the Reddit source code repo I linked to isn't updated any more. Reddit is no longer open source. I assume it has something to do with their proprietary ranking and anti-spam algos getting harder and harder to keep separate from their "core".
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