John Heilpern, in one of his attacks on AUGUST, called it a play in which "almost everything is said." At the time, he was comparing it to the recent revival of Pinter's THE HOMECOMING, in which almost nothing is said.
Shakespeare's plays are classics, not only because they continue to resonate with every generation, but also because one finds something new every time a new production is mounted (or, indeed, every time one of his plays is read.)
I think AUGUST's status as a classic will depend more on whether it continues to work for each generation. But the play is incredibly act-able (will it stand up to different interpretations?), and very able-y constructed, so it's possible.
However, I think we should reserve further judgment until the film comes out: considering how film-able the play is, will it effectively stop all further productions of the play? (I don't think so, but, again, we'll see.)
"Y'know, I think Bertolt Brecht was rolling in his grave."
-Nellie McKay on the 2006 Broadway production of The Threepenny Opera, in which she played Polly Peachum