I'm feeling hopeful that she might be a new party member while also being conflicted with the other Phantom Thieves views. That could add a layer to how idealistic their view is on stealing other people's hearts while not dismissing them as mere hogwash from the public.
Needless to say, it'll be awesome either way.
(P.S. Kasumi seems to have a simple yet sleek character design. I'll probably have her as a favorite.)