I feel like the people who are concerned enough to leave twitter over the direction it's going will not jump straight into another app completely controlled by a single person.
My guess is they will possibly see some growth from instagram power users who are convinced to try it, but I don't anticipate a mass diaspora from twitter to threads.
EDIT: others in this thread are claiming that it may be compatible with activity pub. If that is the case then it may look a little more interesting to those leaving twitter.