Interesting. I had not heard that the artist still owns the Bull. I would assume that he did not waive his moral rights in the loan agreement so it seems to me that he has a plausible basis to make a claim.
As State Street has essentially admitted as much, it also seems like there may be a solid argument that SHE does distort, mutilate, or modify the Bull in a way that prejudices the author's honor or reputation. under the Visual Artists Rights Act. I have not read the claim but I guess it is against the NYC department that granted them the permit to place it there which might force them to cancel that permit, if it is not expired by that time.
But even if he wins, State Street has still pulled off a huge marketing coup.