Maybe a spin-off, maybe even FF VII R (since it's made in UE4), but a mainline title? I don't see it.
From what I could gather, the Switch is less powerful spec-wise than both PS4 and XBox ONE (and their new iterations, the Pro and Scorpio), so making a straight port would not work (never mind that the Switch is built on an ARM architecture, while the other two use x86). What could happen, if Square Enix were to put the resources into it would be something akin to what they're doing with Dragon Quest XI - make a version that is similar in content, but utilises a different look - but that would require them to see enough money in a separate Switch version to make it happen. Yes, they're betting on the Switch already with DQXI, but Final Fantasy's a different beast, plus they can scoop up any losses made there with both the 3DS and PS4 versions of that game probably in Japan alone.
For the time being, I'm on the negative side of the issue of a mainline FF being released on Switch - but Square Enix is welcome to prove me wrong.