I suspect (I sure damn hope) that a lot of instances will move to block pretty quickly when (not if!) Threads gets caught with data it should not be keeping, or using non-Threads data for advertising purposes, or something like that.
My position therefore is: give them a chance. Not the company; no fucking way. The people: for my (and others') friends and family, for government officials, and for various feeds and offices that publish important messages (weather alerts, travel delays, school closings, etc) on platforms like Twitter, #Facebook, and #Instagram, but don't here.
If you want to block #Threads, go for it. That's your loss. If you want to block anyone who interacts with Threads, I mean that's your right and all but that's an awful idea, because it'll probably split the Fediverse into two.
However: I want to know who signed the NDA. Those instances do need to be blocked or actioned against. Their admins cannot be trusted, if they're going to meet with #Meta (!!) and go "all is good"; there's no way all is good when you're talking about Meta.
The only way I'd trust Threads is if they publicly signed a legally binding contract that basically said, we're gonna follow your lead, we aren't going to interfere with development, and we're going to interoperate as well as is reasonable. That would allow them to be sued for breach of contract; although given the money they have, it would have to be an incredible amount, written in the contract, that would kill their business.
cc @stux (this would ping you if you weren't on mastodon)
boosts welcome, respectful disagreement also welcome