Spoke to M. Night who said, "I do intend on making a final Unbreakable movie and I’m intending on doing it next" https://t.co/dXUwdRQ8fZ— Mike Ryan (@mikeryan) January 22, 2017
Mike Ryan is a senior writer for Uproxx and the quote in the tweet is what Shymalan said in their interview together.
SPOILERS FOR SPLIT
If you've seen Split, then you know that at the end of the movie Bruce Willis shows up as his character from Unbreakable and references Samuel L Jackson's character from the same film. So basically Split and Unbreakable are in the same universe.
The ending of Split also sees James McAvoy's killer character running free where he will kill again. Presumably a sequel will involve Willis having to stop him which will pose a problem as McAvoy's character is also pretty invulnerable when he becomes "the Beast".
“It’s the final movie of these two movies put together [...] Yeah, I’m still close to Bruce and everybody,” says Shyamalan. “And obviously I’m still close to James and still in touch with Sam and all that stuff. So, hopefully that becomes a reality very soon.”
honestly, the bigger thing to warn for in Split is the CSA reveal