Merrick here...

While pimping his upcoming console game THE CHRONICLES OPF RIDDICK: ASSAULT ON DARK ATHENA, Vin Diesel briefly alluded to a third feature film's state of development:

Maybe we're too tight-lipped about the next Chronicles of Riddick film, and I think circa the release of [Dark Athena] that's probably when you'll start hearing more about the next Riddick film. It is underway
[EDIT]
David Twohy is finishing up the next script.

...says Vin in THIS INTERVIEW with GameSpot.

We've previously heard indications that a third RIDDICK film might be somewhat smaller in scale than the second installment - which was gargantuan compared in scope when compared to its progenitor (PITCH BLACK). No word on if this supposed downsizing will remain in play.

As for the game: a playable demo for ESCAPE FROM DARK ATHENA is currently available as a free download on XBOX Live. One cool feature o the game = your character's (Riddick's) ability to locate terminals which allow you to assume "control" of enemy soldiers. You can use them to carry out tasks, and even fire on/destroy their own evil brethren.

The game releases in early April for XBOX 360 and PS3. You can find its official site HERE.