Wii U version confirmed to support the 3DS itself as a controller option.
http://www.destructoid.com/use-your-...--281123.phtml
Nintendo's Treehouse is currently hosting their 8-hour live stream of the game.
http://www.destructoid.com/nintendo-...y-281112.phtml
According to Destructoid, World Map spectator mode contains a spoiler of revealing all the hidden characters in the game if its viewed/played before unlocking everyone.
http://www.destructoid.com/super-sma...n-281101.phtml
At least for the 3DS version, it takes around 120 matches to unlock all the secret characters if other modes are not played. In terms of comparisons, only parts of Melee's and Brawl's rosters were unlocked by that point.
http://www.destructoid.com/smash-bro...k-281095.phtml