2015.
WHY?!
I CAN'T WAIT THAT LONG!
It's been in development since before A Machine for Pigs was fully announced. It's been said they already have 3 years into it. They are taking their sweet time. As far as the video they released today, it seems they have a bundle of assets. But if it's anything like previous videos they've done where what is shown is just a tech demo essentially, it will take them a while to get everything pieced together.
Honestly, I think PS4 Europe tweeting the ARG forgeted it up. People in the official discussion topic which Frictional monitors since its on their forum were freaking out assuming it was going to be a PS4 exclusive to the point news sites started reporting it as fact. It got out of hand, and I think they decided to cut the ARG short before stuff got really bad. Even if that wasn't the case, I can see how they'd rather it so they can outright say "PC and PS4."