Starting a test where posts from Threads accounts will be available on Mastodon and other services that use the ActivityPub protocol. Making Threads interoperable will give people more choice over how they interact and it will help content reach more people. I'm pretty optimistic about this.
I have my problems with Meta, but I'm hoping this will help Mastodon grow
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.
Do you want threads to become dominant on the Fediverse by several orders of magnitude? Do you understand the implications of such centralisation on the Fediverse?