As it has a limited budget, the upcoming R-rated "Riddick" only has to pull in so much box office to make a profit. If it does though, then the story can be continued in further sequels.
Originally, filmmaker David Twohy and Diesel had planned for "The Chronicles of Riddick" to be the first in a trilogy (with "Pitch Black" being a kind of "Hobbit"-style one-off prologue). After 'Chronicles' disappointed, plans were changed.
As a result, "Riddick" isn't the second of this trilogy. Rather, it's a mostly standalone "survival story" says Twohy. That said, the mythology laid in the first two films isn't ignored with Karl Urban brought back for several days of filming "to advance it and lay the groundwork for movie four."
Twohy adds that "It ["Riddick"] does play in a gratifying way as a standalone movie, but there are threads that we continue to sew that we started in previous movies and will continue in future movies."
So if they do go forward with a fourth film, what would we see? Diesel says:
"You've got to go to the Underverse. It's expected, it’s something I firmly believe. You’ll have to go through the Underverse to get to Furya. So, those are the two further stories that are mapped out.
The Underverse is a much more costly venture. We went this direction, trying to do an R rated movie, which is cool and even more interesting because it’s so unexpected. But yes, you will be at the Underverse and you will be at Furya sooner or later."