I'm on the fence here. Luckily, at least, I think community/subreddit-based sites like Lemmy/Reddit don't have "network effects" that are as "sticky" as Mastodon/Twitter, because with Lemmy/Reddit you don't need to build up a follower list to start getting value. You just join the community and it's as if you immediately "followed" a bunch of people who share your interests. You don't even need to make an account - you can just bookmark a community and lurk, and maybe you eventually make an account to start interacting. It's a great "on-ramp" - very low barrier to entry/usefulness.

I think that's why Lemmy was able to take off so fast. It relies on community-level coordination, rather than every individual user having to make their own choice to switch, and try to get all their followers/followees to switch. So even if Meta did add a community-style mode, I don't think it'd eat into the Lemmy userbase. It is hard to be sure though, and I respect the choices of those instances that have blocked/defederated.

Mastodon admins have a harder decision to make I think - there's an opportunity to get very quick growth by effectively adding a lot more followable users/content. A bunch of people don't like Meta/Facebook, but want to follow their friends, and so they may use Mastodon to do that, which could get a lot more people to move to "real" fediverse apps/sites like Mastodon. I know a lot of people that are on Threads now, and I'm looking forward to being able to follow them from Mastodon, rather than being forced to get Threads to keep up to date with what they're working on.