Actually, the Official Nintendo Magazine of U.K. had an issue a while back this year, with an article on Luigi. It said he would get a new solo 3D platformer following SM64's storyline.
But, its sort of still a rumour and a lot of people aren't buying it. A few months ago on GameFaqs and other boards, had a lot of people claiming they read it in the magazine, even websites in pure French had people talking about it. The funny thing is that not one person has scanned or photocopied the article, despite all the people on gamefaqs that were going "pics or it didn't happen"
It was even mentioned in Luigi's page for Wikipedia, might still be there, there was a debate about whether to keep it there or not.