User blog comment:SilverthehedgehogMan/Smash Analysis: Who May Return in Possible Future Installments?/@comment-6684591-20170603053347

I think Marth has a higher chance than you might think, because Sakurai stated in an interview that he actually wanted to include Marth in Smash 64, which would've made him a member of the Original 13, I guess. Since Sakurai wanted to put him in since the beginning, I'd say it is almost certain that he will be returning.