I stated this before, but I'll do it again.
I don't see Mr. Glass as an enemy for David Dunn. Mr. Glass did terrible things to the world to forfill his quest, to find the unbreakable person. Now that he has found him, he is done. He was supposed to be a guide for David, but in the twist we found out that Elijah is a terrible person. The only thing that I can think of is that Mr. Glass breaks out of jail and runs away, but not that he contineus his evil deeds.