It appears that the upcoming sequel to Luigi’s Mansion, Luigi’s Mansion: Dark Moon slated to be released this March will possibly feature a multiplayer mode.
The official website states in the game’s description,
With so many new places to explore, all new ways to capture ghosts, and a brand new local multiplayer mode, Luigi’s Mansion: Dark Moon is another star turn for Mario’s heroic brother—and it’s only on Nintendo 3DS.
However, in the product details it says “No. of Players: 1 player” which contradicts what the description says. Nintendo, however, has not officially announced any details about a multiplayer mode yet but that might change very soon.