Probably an NX game, hence the 'hope to unveil in one year' wording. It probably isn't for the bone because that would just be career suicide at this point, with that console struggling to sell triple digit units weekly in Japan which I'm assuming is a target market for him. If it were a PS4 game he would need a publisher and Mistwalker have yet to make a game with any third party for console.
Mistwalker has been around for about a decade now and have produced three console games. Two published by MS and the third published by Nintendo. But not one third party publisher have made a game with them, why is that? You would think a studio like Mistwalker, with Sakaguchi and that famous composer whose name escapes me, would have been able to secure a publishing deal with a Japanese publisher, especially after the praise for LO and LS. Is his reputation still tarnished by the spirits within, is it because of his history with MS, is he difficult to work with? It's baffling to me that someone who was behind some of the best games made during the golden years of the nineties is not regularly pumping out games with a Bandai Namco, a Tecmo Koei, or some other third party.
Or is the real reason that all those publishers would want a PS4 version of whatever he makes and Sakaguchi is still holding a grudge against Sony such that he would rather not make a game at all than make one on their platform... and thus we have him making games for MS and/or Ninty once every five years when they have an extra couple bucks to spare.