This is in contrast to Mastodon where people were told to pick an instance and not really guided to any one as the primary one (because Mastodon devs/users don't want there to be a thought that there even is a "primary" instance).
People here on HN can claim picking an instance isn't a big deal all they want, but I can say with confidence it is. I'm in various furry artist Discord servers where people expressed their distaste for having to deal with the multiple instances.
Take that away you’re really back to “just Twitter” with fewer features and less content.
I agree that algo and client choice would be a positive for a mature site like Twitter, but it’s unclear how a site with this strategy will get enough traction for the choices to be useful