I just can't see them adding a guest character who's entirely obscure in Japan.
Like honestly, sometimes I think the only reason Rayman even appears in Smash at all is because Rayman Legends was actually Wii U exclusive and Nintendo published in Japan. Notice how of Rayman's representation in Smash is based around Legends.
Also Ubisoft leaker mentions that Ubisoft actually comes to Nintendo and Sakurai to ask them if they could add Rayman to Smash Bros. And basically Sakurai said no? but they were willing to donate the models for trophy.