I really do think it would perform fine on the Switch as long as the proper concessions were made. It would definitely sell well on the Switch, so I would like to see it on the Switch to open a new audience and take it on the go.
That being said, yeah I see why it hasnt been on a Nintendo home console yet.
I don't believe there's a precedence for a game that looks like this and struggles to reach 30fps on PS4 (at least the pre-release build), making its way to Switch. The most impressive port according to Digital Foundry (Doom) had the visual downgrades accompanied by the framerate cut in half. And that's usually the case, but it's not an option in a game like this.
SE said they were looking into if FFXV could work on Switch around a year ago, and if something like that comes to Switch, I'll amend my expectations for future ports. But until then, I don't expect to see them there.
Square haven't even gotten Dragon Quest XI to work on Switch yet, and they announced it for Switch in 2016.
But I'm sure KH3 would sell well on Switch, if it was on the system. Just like Monster Hunter World would.