Seems George Lucas isn't quite "there" yet when it comes to this one. Suppose you could argue he wasn't quite there with the Kindom of the Crystal Skrull either.
Recently, Spielberg told EW, "We have already agreed on the genre of the fifth movie, we already have a concept in mind," but when Vulture caught up with Lucas last night at the premiere of The Adventures of Tintin, Lucas admitted that the concept wasn't quite fleshed out. "Actually, I told him I didn't have it yet," Lucas said. "I told him about the story, but I really haven't found the MacGuffin yet. I mean, I know what it's about, but I just have to find a MacGuffin that fits into the arena we're working in." Will Indiana's considerably extended family factor into the movie? Lucas just laughed. "Yeah, we'll see!"