Xenoblade is the only IP in the history of Smash Bros that was released after the previous Smash Bros game (Pikmin and Wii Fit are close, but came out a month before Melee/Brawl).
Character wise, only Shulk, Greninja, Robin, Lucina and Dark Pit were invented after Brawl. 2 of those are clones. Brawl had Lucario, Lucas, Toon Link, Zero Suit and Ike. Melee had Roy and Pichu.
The majority of new comers to Smash are older characters (Brawl was kind of close, with a little less than half). Smash 5 is especially going to have issues, because there's no real major holes missing or glaring omissions. At least not enough to build a roster out of if they start plucking ideas like Dixie or Dark Samus out of Smash 5.