Also, I read that threads is connected to the technology behind Instagram, which is why they can share data back and forth. If you think about it, Instagram already has a fair amount of the technology well in place, for posting images, text, and videos of a limited length.

Given how long that code base has been alive, it seems unreasonable to think they could simply "wedge" Twitter code in to replace assets they already own without completely blowing things up.

They've likely been working on it for a while, and now is the time to pounce.