Apparently there is a rumor to Luigi's Mansion in the works, and it is slated to appear on Nintendo's upcoming Wii U console. At least, that's what one online retailer seems to believe. The website Play.com has listed Luigis Mansion 2 as a title available for pre-order on the new home console. Nintendo has not made any sort of official announcement about such a game being in the works.
However, the company has confirmed that Luigi's Mansion 2 will be coming out for the 3DS. So what this means is that either Nintendo is working on making it multi-platform for its new console as well, or someone over at Play.com is just confused. When an online retailer adds a new title to its database, sometimes it is based on conjecture, sometimes it's based on a private conversation with a publisher, or sometimes it's just a mistake. It could be any of the above.
Luigi's Mansion has a somewhat interesting history. It was a launch title for the Gamecube, and it scored a fairly strong level of sales. But that is partly because it wasn't until much later in the Gamecube life cycle that Luigi's much more popular brother, Mario, got his own game on the platform. There was a new Luigi's Mansion game that was on the drawing board for the Wii, but that would have included a 3D display periphaeral that ended up not panning out.