If you're hoping for a third Dead Island entry, you might be in luck. More zombies!
"I would not expect the series to stop at this point. :)"
He didn't go into detail, but he did say that if a follow-up title emerges, it'll be in the same style and structure as past iterations; i.e., open-world craziness. He specifically mentioned Day Z and said that not everyone wants that sort of linear experience; some want to feel part of a larger world. I sorta thought everyone these days wanted the "larger world" and almost nobody left wanted the linear approach, but whatever. Eickmeyer also added that a Hawaiian setting "would be awesome" but nothing is concrete as of yet.
Well, Riptide sold pretty well, so why not?