@darnell I don't believe for a second that Instagram or even FB not joining the fediverse is about technical unfeasiblity. Sure, it might be a lot of work but at the end of the day the main reason is Zuck just doesn't see how it would benefit him to open them up for competition that way. Meta was built on walled gardens.
I'm cautiously positive about Threads being a good thing for the wider fediverse but we can never forget Meta is absolutely not a company that is in it for the greater good, only for their own direct benefit. They will drop ActivityPub the second it suits them better than being a part of it.
My hope is just that that moment will never come and threads either does not eclipse the rest of it or withers away eventually after having helped the #fediverse grow.