The book first appears in Harry Potter and the Philosophers Stone as one of Harry's required books for study, it is supposedly written by magizoologist Newt Scamander and based 70 years before the events of the Harry Potter series so unless it is done in some sort of narrative fashion it's unlikely that Potter and the gang will appear.
J.K. Rowling, although overseeing the mega successful Potter series of films didn't write any of the screen plays, but she has done for this, and as this New York Times article points out, it was a favour for CEO Kevin Tsujihara.
No word on any details so far except for the trilogy aspect of the film, another multi billion dollar series of films in the making? Lets just say The Hobbit!