There aren't really any updates as such in this (very) home-made video of Vin Diesel and director David Twohy discussing **Riddick 3. But it's a while since we heard any new news, so it's evidence at least that the project is still going ahead.
Apparently put somewhat on the spot by his leading man, Twohy repeats the previous mantra that the follow-up to Pitch Black and The Chronicles of Riddick (not to mention two rather good videogames) will be far closer in spirit to the former than the latter, not least "because of the money involved. We want to maintain our R-rating, at any cost. And that cost is a lot!" he jokes (meaning that an R-rating dictates a budget drastically reduced from Chronicles). "It's going to be tough, and it's going to be lean, and we're going to be quick." He also promises "seduction"...
Last we heard (a year ago, from a source who'd read a script of unknown draft number) Riddick 3 begins with a battered Richard B crawling on the ground of his desolate home planet Furya, and sees him fighting indigenous aliens and fending off bounty hunters. Is he still (ahem) Lord Marshall of the Necromongers? Will Karl Urban be in it? All will be revealed at some point as yet un-established.