In a recent column in the weekly issue of Famitsu, Sakurai shared some details about the decision to keep veteran characters Ice Climbers out of the two upcoming installments in the Super Smash Bros. series.
As it was mentioned earlier on in development, Sakurai was having trouble running the pair on the 3DS version of the game. The team did get the characters running on the Wii U version, but given that the Ice Climber series has not gotten any high priority recently and was not set to have any new installments in the near future, the characters were cut from the game.
Also of note, Sakurai mentioned that if both games were to be released together, the games would not have seen a release date until 2015. Debugging is why the two games needed separate release dates. Sakurai also mentioned that Akihiro Toda, responsible for the texts in the Mother series, worked on the trophy descriptions in the upcoming titles.