The storyline will supposedly be announced within the next few weeks, but at this point, it is considered rumor. Here is the supposed leaked plot:
"Ron Howard is making a movie about the Bluths using an A-List cast. But Dr. Tobias plays himself because nobody wants to play him in the movie. The Bluths decide to make their own movie in contention with Ron Howard's."
Mitchell Hurwitz had previously mentioned that he would like to see Maeby create a self-referential movie about the family, so this could turn out to be the real deal.
No production date has been set.