If Meta is really working on a new ActivityPub-powered social network, I see it as a very positive signal overall--my personal feelings towards Meta notwithstanding. For one, it's validation for our entire ecosystem from the biggest player. It also tells me that they don't see themselves as strong enough to keep users locked inside their walled garden anymore. It means the tide is really turning for interoperable social media, and that's always been the goal.
@Gargron I suppose meta could create their own gigantic (and modified) Mastodon instance and brand it as Facebook. They may even try to contribute to Mastodon’s source code and ultimately try to steer its development in whatever direction they want.