The website sourcegaming has apparently data-mined Super Smash Bros. for Wii U and found what appears to be a plethora of information that implies a bit of content was removed from the game.
First of all, there is a stock holder that seems to show the viruses from Dr. Mario. The stock holder is the same that other enemies, like Ridley and Metal Face have, so the presence of the viruses seems to suggest Dr. Mario was going to receive a stage and they were going to function as hazards or boss characters.
The data that was mined also has references to ‘rhythm’, which has led people to believe there was supposed to be some sort of representation from the Rhythm Heaven series in the game. This fits alongside the original Smash Bros. leak, Gematsu, which stated the Chorus Kids from Rhythm Heaven would be playable.
Another interesting reference is ‘plankton’, which many believe refers to Electroplankton, and therefore the stage Hanenbow was set to return (for some reason).
Check out the rest of the data here.