Wow, so WhisslBlank decided to go all ham now. Simon feels like a easy character to piggybank off of, and K. Rool's popularity was big enough to go out on a limb on. The only reason the neogaf leak lives to see another day is cause it accurately predicted Chrom being a Roy echo, something I don't think anyone saw coming. If it's fake, I can just imagine the user thinking "oh snap, it actually happened! Okay, let's go all ham now!" But that said, for all we know, he could be legit, and I don't think the expanded "leak" is totally out of question for a couple reasons.
Sakurai mentioned Terra during a famitsu interview, saying: "But on the other hand, if you think about who to add from Final Fantasy, it’s hard to come up with a choice that’s not Cloud. We could have used Terra or Bartz, protagonists in their own right, but I feel like there would be some people who wouldn’t know who those characters are."
Source:
https://sourcegaming.info/2016/01/20/sakurai-x-nomura-creator-interview-2016-part-one/
Just a name drop. I think Cloud was the only character he was really considering, but who knows.
Meta Knight isn't on the Smash Ultimate demo roster. I don't think we've seen all his alts in Ulimate, have we? Similarly, Samus didn't have her Dark Samus alt anymore, and we now know that's cause DS was becoming a full on echo character. If we can get visual of Meta Knights alts in Ultimate, we could maybe debunk or further credit this rumor rather quickly.
Regardless of what's true or isn't though, I just want Isaaaaaaac! I don't really care who comes with him. :D