I guess that will stay a wish. You'd mostly be able to test HTML exported games if the Switch browser is powerful enough to handle them.
Developing (and publishing) games for the Wii U required you to sign up for the Nintendo Developer Program and sign an NDA about the tools used which also includes the Unity add-ons. I don't know if Nintendo contacted Unity or Unity contacted them to develop that add-on, but if Nintendo contacted them, I doubt they'd be interested in Godot at this time.
Beyond that, you can't just run games developed with Unity on your retail Wii U - you'd have to buy a CAT-DEV or CAT-R which is basically a developer Wii U console - it'll be similar for the Switch - and those cost around (refurbished) or more (new) than 1000$.