XON WIIU doesn't work on the 3DS version in any region, including Japan, because its purpose is to enable Wii U only functions. The benefit is that now XON WIIU isn't a syntax error, it just fails when you attempt to run it. Hence, Japanese games that have a 3DS or Wii U mode depending on hardware will actually work now, rather than fail with a syntax error and require commenting it out.