It is a rumor. I wouldn't take it too seriously. It is way too vague. Anything that cannot provide an answer to the basic questions of when? where? how? why? should be seen just hearsay. This is pretty much the basics for sorting old chain-mail urban stories from real events. I am actually surprised this gets pushed by many to imply that it is a fact.
Who knows, maybe this rumor was implanted because Square Enix and Nintendo are trying to get people off the scent in order to bring genuine surprise to the fans once the reveal comes. But just like many assumptions, this is more wishful thinking than based on anything.