It's important to note in the case of Ike that the roster was finalised somewhere around 2005 with one obvious exception and Ike himself is heavily derived from Path of Radiance which was released around the same time, meaning he had extremely good timing similar to the Awakening characters
(Sakurai himself stated that had Awakening been released several months earlier or later, Robin might not have made it in).
No, but it's also not hard to believe that he might not have had a Xenoblade placeholder. You have to keep in mind that historically, Xenoblade has not had a newcomer for every single game and situation it had a chance to, seeing as Elma wasn't a DLC newcomer for Smash 4 despite good timing, meaning it is not guaranteed that the idea of a Xenoblade 2 character would necessarily be high enough priority for there to be a placeholder, at least whenever the roster was finalized.