Taylor Sheridan looks like he has another hit on his hands with “1923,” the second prequel series to his TV sensation “Yellowstone.” And there are even more “Yellowstone” prequels on the way: “6666,” set in modern-day Texas, and “1883: The Bass Reeves Story.” But the most exciting upcoming Sheridan project may be one no one knows about: a show he’s shot secretly with some huge movie stars.