inspired by Split I actually rewatched Unbreakable for the first time in eons a could days ago. The "twist" in that is so low-key it barely even registers as a twist. it just feels like a good ending.
Likewise the "twist" in Split barely registers as a twist. It's just a bonus little epilogue in the last 30 seconds. It doesn't radically change anything about the movie you just watched, but it does enhance the story since it turns it from a movie about a guy with a version of dissociative identity disorder that is medically inaccurate in every way, to a movie about a guy who exists in a world where powers are possible and he's developing his powers. Some of the themes of abilities being a new phase of human evolution overlap between both films too.
It also frames Split as an opposite to Unbreakable in that Unbreakable is the origin story of a Superhero and Split is the origin story of a supervillain. Stylistically the films are very different though. Unbreakable is a moody drama, Split is a thriller with comedic elements.
Supposedly Shyamalan's idea is for his next film to be a combination sequel where McAvoy and Willis are pitted against one another or something like that. I think that would be pretty cool. Should we risk giving him a big budget again to make that happen? I dunno.