Good news: This will result in more average-user understanding of the fediverse, getting past the consistent issue of people not understanding it. It will increase the Fediverse's usershare by a considerable amount. And to top it all off, it will probably cause a snowball which will make the Fediverse as a whole eclipse twitter.
Bad news: This is being done by facebook, willingly. Any company that is taking action like this is doing so for their own benefit and no one elses. This may be detrimental to the Fediverse in the long run if users opt to all just jump on to Threads because of some obnoxious 'Embrace, Extend, Extinguish' tactic they may or may not pull in the future.