What are your reasons for speculating that Rituxan is not one of the first three FoBs in the MNTA/BAX agreement?
If they are indeed confident of being able to develop interchangeable FoBs, then Rituxan would seem to be an obvious choice. Even with the availability of non-interchangeable FoBs, Rituxan could still be a blockbuster product - unless you believe that biobetters such as obinutuzumab will supplant Rituxan.
i would venture to guess that Rituxan FOB development by BIIB violates BIIB's contract with Genentech in regards to each party doing whats in the best interest in the product.