I do love this "if Marianne hadn't died" scenario for Cornelia. I don't think it would be a bad idea to have people from different verses if you want to go with this.

But I am also intrigued by the idea of the vis and Euphie going to Japan should Cornelia take her GG position early on. Lelouch would probably relish the chance to gain first-hand knowledge of the rest of the empire, and it might still be difficult for him to have the access he wants at his age.