Think you missed the plot at the ending, they introduced the clover foundation and the three head characters whereby they build up for more following films. The son of David, The mother of Elijah and the girlfriend of Kevin. Like Mr Glass said: "This is not a limited edition, this is the origine".
He said that, you are right @keyserowze. But i thought Glass was he end of a trilogy.
You think we will see some more sequels out of that universe?
For now its unclear, think it depends if the movie will sell like they expected. but the clover foundation is explained and new stories can easily been created now.