“Basically, you’ll see The Witness on PS4 before you’ll see it on the next Microsoft console or on the Wii U, presuming we eventually do ports to those consoles. Ideally we want the game to be in as many places as we can get it, but since we are a small developer and it’s a complicated game, we can only do so much at once.”
Basically it’s all based on whether the game is successful or not. If the game sells well, chances are that it will be released to other consoles. If it sells badly, well, then you will have to get a PS4 to play it.