Hasn't it already been established that threads would most likely deathhug most of the fediverse? It's content would be overwhelming and nothing could keep up with it. I'd rather have the fediverse be a more small scale, cozy and niche place*.
But considering that the majority of instances have already blocked threads, there would not be much of a fediverse to federate with anyway once/if they do.
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.
Kinda refuse to believe that every single person on threads is going to post low quality content. I'd argue that content made by a bunch of people not constantly thinking about the fediverse will help the fediverse. Let's be honest, lots of the content posted on fediverse apps are somewhat forced because we all want this to work.
It weirds me out that the discussion has moved to "quality of content" when that wasn't the problem with Meta/Facebook embracing the "federation" (ActivityPub).
The problem that got people worked up is that there's a history of big companies stepping in, benefitting from open protocols, and then essentially hi-jacking them. A common example would be Google doing it with XMPP, but similar things have happened, not to protocols, but to FOSS in the past. Like with Oracle buying SUN and essentially killing OpenOffice, causing people to fork it to LibreOffice to continue the product.
You also saw it a lot in the early days of the web, with the "browser wars" where Microsoft behind closed doors, added features to HTML and JS that other browsers then had to rush to implement. Companies have done it to one another too, Microsoft reverse-engineered AOL's AIM to make MSN Messenger compatible with their protocol, so AIM and MSN users could chat. AIM didn't like this, and it resulted in a long back and forth, until Microsoft uncovered that AIM was using a secutity exploit in the AIM client to authenticate, and eventually acted whistleblower on this.
Facebook/Meta doesn't want the federation, they just want the users, or more accurately their data. They'll happily federate and contribute until they feel like they've gotten enough from it, at which point they'll pull the plug.