I think it will too.
Even if they have to rework it a bit Switch apparently works well with Unreal Engine 4. Yes they'll probably have to downscale assets, but KH3 on Switch likely adds an additional 1+ million WW without much fuss I would think, and might even be the better selling version for the Japanese market.
It makes a hell of a lot more sense than a XBox One version.
They're already doing it for Dragon Quest XI (Unreal Engine 4 game). In fact this may have been one reason why Square-Enix dumped the Luminious Engine for Unreal Engine 4, so that they could cash in on future Nintendo portables (they likely knew about the Switch a while ago seeing as how they announced the first game for it).
They need it to run, but they can strip it down quite a bit for Switch, portable mode could be 960x540/30 fps with no AA and downscaled assets and probably still look fine on a small screen. Docked mode could run at 720p with maybe a few added effects if they really care to add them.
