Unfortunately Facebook will most likely pursue their usual goals of mass user attraction, followed by user domestication and enshittification. They'll try to attract as many Fediverse users to Threads as possible, then slowly make it a shittier and shittier experience to use Threads unless you have an account there or something, and their federation will get worse and worse until they'll just split off, but this time taking a shit-ton of Fediverse people with them (who will now likely have higher switching costs due to the network effects exploited by Facebook). Not to mention that Threads will be trying to collect as much data about everyone as possible (including those who just have an account on a federated instance), and will probably try to send out ads to federated instances.

It's possible that Threads will attract more people to the Fediverse. It's at least as likely that Threads will end up pulling people from the Fediverse, and into an eventual walled garden.