User blog comment:The Puffle Planet/Possible Leaked Lucas, Mewtwo and Wolf DLC?!/@comment-24858759-20141003100330/@comment-4115159-20141005213741

They also said they weren't gonna make the 3DS version if it was in any way gonna hinder the Wii U version. If the Ice Climbers are out it would have been because of a choice made before the 3DS version was considered. Not because the 3DS can't handle it.

But who knows. As far as I'm aware Sakurai said that both versions would have the same amount of characters. But he did not say they would have the same characters. Ice Climbers could still appear in the WiiU version.