In an interview on the Huffington Post, they spoke very briefly about it:
There’s been talk of an “Unbreakable” sequel for a long time.
Yeah.
Samuel L. Jackson seems to want to do it. I saw you two talking on Twitter.
It’s a harder one for me because — it’s getting closer, by the way.
I feel like I’ve heard that for the past 10 years. I want that to be true.
I want it to happen, too. […] So, slowly I’m getting a story in my head that I feel like is able to tell what I’m feeling right now.
For people who like that movie, it sounds encouraging.
Yeah, it is! The story of a guy who kind of wakes up with a little gray feeling in the morning, I love that character. It’s something that I feel and I want to talk more about that character.
-via Huffington Post