Even the second half of 2018 seems unlikely. For the game to be of high quality, open world exploration, highly cinematic, and a complex combat system...you are going to need at least 4 and a half to 5 years, development time. Unless you have a large development team and I believe the dev team is pretty small. Anything shorter is going to feel rushed, or lacking depth.
We'll see how it turns out, but I have my doubts. It just seems too fast. And the story isn't even going to end for God's sake!