Super Smash Bros. on the 3DS, which was just released in North America yesterday, has a day one patch to enable multiplayer. Nintendo's support site also states that in the update "Adjustments have also been made to balance the game and make for a more pleasant gaming experience." You can still play offline without applying the patch, but Nintendo strongly recommends players apply the patch. Nintendo also assures players that downloading the patch will not affect player's save data.
Nintendo has not yet announced a specific release date for the upcoming Wii U version, which is scheduled to release in 2014.