Dragon Quest is a Playstation and Nintendo series.
Final Fantasy is only a Playstation series.
I doubt that Final Fantasy XV and Final Fantasy 7 Remake will be on NX.
Would they even be possible on NX?

Nintendo has to do more than great 1st party -- I think they could rekindle the magic the SNES in which the highest quality titles included both 1st and 3rd party games.

False. Final Fantasy started as a Nintendo home console exclusive and was very sorely missed by many Nintendo gamers when FF7 went exclusive.

Over the years, Nintendo's had a few exclusive Final Fantasy spinoffs and remakes on home console and handheld. The hardcore fans of FF are on both NIntendo and Playstation.

If DQXI is a port of the PS4 version, and NX has X1 level specs, FFXV and FF7 are certainly possible. Likely even more marketable than X1 versions if the NX gets a proper start.

I know somebody would quote me! 
I wrote "Final Fantasy is only a Playstation series" and not "Final Fantasy was always a Playstation series". There is a difference!
As long as Nintnedo doesnt't get a real Final Fantasy game, Final Fantasy isn't a Nintnedo series.

If they make a popular platform that's a similar architecture and spec to the PS4, they wouldn't need to be planning collborations. Devs would just port to their console by default.

Nintendo had no third support with the Wii, and no third support with the Wii U. I don't believe (now) that NX will have a lot of third support.

Like already said, DQXI is only considered, nothing sure yet. If the NX bomb like the Wii U, you can't await a lot of games on it...

(without even talking about power, because we're not even sure that the NX will be as powerful as the PS4. I'm pretty sure it won't)

Can it run them though? We do not know yet.

For all we know the NX is being considered for the 3DS version of DQXI

You make it sound like it is exclusive to the NX.... lol.

FF7:RE, if it comes on the NX, will not be a system seller. Just like how Assassins Creed 5 is not a system seller for ps4 or how Batman Arkham Knight is not a system seller for XB1.

The game is now exclusive with ps4, markets with the ps4 and people associate it with the ps4.

It would definitely be huge to see Final Fantasy return to Nintendo. Now imagine if Kingdom Hearts 3 also did?

While FF is an important series to have... NX needs more high profile western games like the next GTA and the GTA after that and etc. And if it does somehow get it, I will shit my pants and eat that shit cause that means that Nintendo is doing the console right