Well yeah it was officially green lit in October but I doubt he'd have even started if they hadn't promised him something along the lines. The ending is terrible at this point. How would that look on Master Villeneuve's vita?
I also doubt they'll go for 3 because all following books don't have that kind of action flick / visual extravaganza potential and this is what Villeneuve can do. Instead there is a lot of talk and this is what Villeneuve can't do. It'll still be the same ol' Dune with a lot of chamber play. I doubt he's even seriously interested in that.
I dunno, I think Messiah works as an ending to the trilogy. There's quite a bit of intrigue and action. Nothing gets too weird—Duncan's Ghola is the only new sci-fi addition.
Children takes a sharp turn with the whole possession thing and then Leto's metamorphosis. But Messiah is quite adaptable and is the real ending for many of the same characters as Book 1.