I didn't have time to read all of the comments in depth but I am not sure if anyone made this connection or not ---
Notice how when Kevin/McAvoy goes to morph into the Beast, he lays a bouquet of flowers down in front of the train tracks, and then proceeds to make his grand change within the train car completely alone-- meanwhile, Unbreakable began with a train wreck, Dunn/Willis the only to survive...
It's really late and my brain isn't totally formulating properly but this could be something that is tied together in the storyline for Glass.
I just got done watching Split and I need to re watch Unbreakable to really try and piece things together but I figured this could be a good place to start.
Thoughts?