Square Enix will likely want to make money off Final Fantasy 7 Remake; selling the game on Switch is a good way of reaching profitability.
Making the game turn based on the Switch will probably allow them to put the full game on the Switch at close to PS4 quality.
With a turn based game, the developers can control: the camera, character movement and pacing with ease.
This should allow the developers to optimise the game enough to be run on the Switch.
Square Enix put Final Fantasy 15 on mobile.
Final Fantasy VII (original) was turn based.
Square Enix has a decent portion of their fan-base who want more turn based titles.
Bringing Final Fantasy VII to a Nintendo platform is a huge PR win.
Square Enix can, hopefully, consolidate the marketing and development of the two versions.
The Switch has massive traction in Japan.
Even if Square Enix has an exclusive deal with Sony: a FF VII Switch, using assets from the Remake should hopefully be possible.
I think there is too much going in favour of a Switch version; Square Enix, almost, cannot refuse.
Also, exclusivity sucks:
It is like an insurance company granting you a new hand: on the condition that you only use it to work in their office.
You can't even take that hand, and use it for your own things: outside of work.