The Nintendo Switch charger isn't standards compliant, and if you use another charger, it might not be able to keep up with the power draw of the Nintendo Switch.
It will be. Supporting USB PD over USB-C is mandatory if they want to keep selling in EU. Nintendo is more than welcome to subvert EU's requirements and find out how that goes.
Probably it will work for the "Switch 2", if there will be such a product.