Noah Baumbach (Greenberg) had an excellent cast lined up for his next feature: Ben Stiller, Greta Gerwig, James Franco, Cate Blanchett.  It is with great regret that I use the past tense.  Scheduling issues kept Gerwig from committing, and Just Jared reports that Franco and Blanchett have dropped out.  Filming on While We're Young was set to begin in New York in June, but Franco will be busy shooting Oz, the Great and Powerful.  Blanchett's motivation is not specified, but it's possible there is overlap with her time on set for the sure-to-be sprawling production on The Hobbit, which starts shooting later this month.  More on While We're Young after the break:While We're Young is about “a free-spirited Brooklynite twenty-something couple who inspires an uptight documentarian (Stiller) and his wife to loosen up — with comedic consequences.”  Franco and Gerwig would have played the twentysomethings, Blanchett would have played Stiller's wife.  Stiller remains attached, and the filmmakers still have a couple months to secure a supporting cast in time for the planned start date.  But it will be interesting to see if this talent exodus negatively affects development.If While We're Young does for some reason fall through, Baumbach has The Emperor's Children and a producerial role on Squirrel to the Nuts to keep him occupied.  Stiller, meanwhile, is currently filming Tower Heist with Eddie Murphy, Matthew Broderick, Tea Leoni, Casey Affleck, Judd Hirsch, and Alan Alda.Franco has many projects on the horizon in addition to Oz -- his 2011 movies include Your Highness (April 8 ) and Rise of the Apes (November 11).  Blanchett will next be seen in Hanna (April 8).