I would caution people to not assume more villains are coming just because of Sephiroth. Reminds me of the "Heroes VS. Villains" theory waaaaay back during early pre-release.
The only thing that immediately comes to mind in regard to Sephiroth and patterns is the fact that him and Min Min both represent a series that had a very minimal to almost non-existent presence in Smash, offering a "second chance" for content, if you will. Does this mean the last three characters will do this as well? No, but if you want to look at precedents, I think this is really the only one Sephiroth makes interesting.
EDIT: I didn't mean to say Chun-Li, I meant Min Min, but Chun-Li was on my mind because I've been theorizing stuff for her a bunch lately. Blegh, stupid brain.
However, I will say that Sephiroth does make things interesting for Chun-Li as well. March is gonna be interesting...