The guy that played his son & the actress that was Mr Glass's mother are both reprising their roles for this film
From what I've read, Paulson's character is a psychologist who treats people who think they're superhuman. I'm wondering, since Glass is already incarcerated & probably getting treated, maybe The Beast also gets captured & held in the same facility. Somehow, Glass sells David out, just to get him locked up as well, just to see what happens.
I think there's going to be an interesting dynamic, because I firmly believe that The Beast's origin is directly related to the train crash that Glass caused. I also believe in the theory that the kid who was being abused, that David sensed, is also the a younger McAvoy. So while people are excited to see a showdown between David & The Beast, I'm interested to see how The Beast reacts to the man that killed his father & set off his life of abuse.