Giving my two cents here, I think Sephiroth is actually the most likely Square character out of all seven. Why? Easy job, most people that know Cloud know who Sephiroth is, we're talking about a Bowser-tier villain in video game history, and seniority is what got many of these guests in to begin with. I think many people are sleeping on him because Cloud's in, but then again, remember when everyone thought that there wouldn't be more than one character per company? Or when they said the same for franchises? We have Ken and Richter now. "But they're echos!", these limits can be broken so long as Sakurai wills it so. Some people also mentioned that the Dragon Quest characters have more mentions, but as far as I've seen, they do it only when grouped together, Seph probably has more mentions if we count them individually. Not saying they can't do Erdrick, Sora, or even Geno, but fame takes precedence, more so if the character gets announced at TGAs.