Assuming Nx comes out in 2016, It has a good chance of releasing on it.Nintendo has a great relation with SE, and it seems SE is marketing the hell out of FF15, so making it on NX would be logical.Imagine if Nintendo managed to make it as a luanch title, and have it announced before it releases in other consoles.Could be big!So yeah, I would say its likely.

But if its launch(on NX) were announced before it released on the other consoles, and that this version were better, as having better graphics, performance, or even one or two exclusive content(probably Nintendo themed)?It could still have really good sales, even if it released 2 months after the release on other platforms

Heck, if it comes out on the NX, I'll buy it xD

I think if it does we'll know at E3. I'd prefer a Bravely NX though.

I'm not expecting it.

If anything, VII Remake seems more likely considering the fact that Cloud was added in Smash Bros.

Maybe a portable version 10 years from now.

I think we need to know what is the NX in first place

No chance. There hasn't been a mainline Final Fantasy game on a Nintendo home console for 20 years. The NX is coming in mid-generation competing against a userbase of well over 60 million(PS4 and Xbox 1). Nintendo's last home console was a flop. Third party titles tend to sell much lower on Nintendo consoles compared to Xbox and Playstation. Even Square's Western/US flavored titles like Hitman skip Nintendo's consoles and the US is Nintend biggest market. Do I need to go on?

Even then, if NX is successful, and remember here that successful dosent mean 100 million units lifetime sold, it will get games from everyone.If NX sells, it dosent matter if the last console was a flop, or if FF hasnt been at a Nintendo home console for 1000 years(this argument is so flawed by the way) or even the mythos that third party sells bad in Nintendo consoles.If NX succeeds, they will get it.

The nx needs it, if it has ffxv aswell it will be a sign that third party will get serious about it.