Vin teases that David Twohy, the writer/director of both Pitch Black and The Chronicles of Riddick, has challenged him to create three different body looks for the third Riddick film. There will be the ripped Dom (aka Fast and Furious) look, the "lean" Furyan look, and the "DiNorscio" look.
DiNorscio refers to Giacomo "Jackie" DiNorscio, a real-life crime lord played by Vin in the 2006 film Find Me Guilty. Vin sported hair and a suit in the role which may be what Twohy is referring to.
Attached to the Facebook update is a 2010 dated image of Riddick titled "Riddick Returns." It's likely fan art and not part of pre-production but I've included it for you to check out below regardless.
Based on this update, it can be assumed Twohy is forging ahead on the next Riddick story but a script is not yet locked in. Vin will surely pass along more updates as he sees fit.