I read on some sites that besides Mewtwo, Lucas, Roy and Ryu, there will be only 6 DLC characters (on the 3DS, maybe there are more on the Wii) The just-announced Cloud is one of the six characters.
If you sort the roster properly, there must be exactly six characters are placed:
Color codes upper picture:
Blue = character available from the start
Red = character to be played first
Yellow = DLC character
NOTE: The characters with the smashball icon are characters which we do not know.
First row: Mario = we may get a DLC Mario character (Captain Toad?)
Second row: Donkey Kong / Zelda / Metroid = We will get a DLC character from one of those series (King K. Rool / Impa / Sylux?)
Third row: Kid Icarus / Fire Emblem / Punch Out / Not presented series = we get a character of this series (Viridi / Tiki / Glass Joe / Inkling?)
Fourth row: Kirby / Star Fox / Retro / F-Zero / Not presented series = we may get one of these characters (B. Waddle Dee / Wolf / Balloon Fighter / Black Shadow / Chorus Men.?)
Fifth row: Pokémon / Earthbound / Animal Crossing / Not-presented series = We get a character in this series (Pichu / Isabelle / Isaac?)
Fifth row: Pikmin / Wii X / Xenoblade / Third Party / Mii = cloud filled the free space, which means that no other character come out of this series.
This is my theory with regard to the DLC.