I didn't see this being discussed anywhere else.
Duncan Jones was giving an interview and said the following:
I had been kind of bummed that the movies didn't work out, but if this is the direction they were going, I am kind of glad there was only 1.For me the story was about Gul’dan and taking the false walls. The symbol or the tribe that he was the chief of, taking them away from the world that was dying on setting them up with a, new home on this, planet of Azeroth. And, really that was going to happen through his baby son who’s, for those who are lore junkies, was getting to grow up to be this character called Thrall.
http://collider.com/duncan-jones-int...rogue-trooper/