I'm serious as a heart attack. Maybe at the end of Riddick 4, he ends up making it to his homeworld Furya, which it turns out has been colonized by xenos. Maybe the Necromongers had such a hard time with the Furyans that they resorted to using facehugger eggs they'd found on LV-whatever as a bioweapon. Riddick has to escape with what's left of the Furyans in an exodus..or more like an anabasis (they'd have to fight through not just xenos, but feral factions of Furyan survivors too).
Someone who's a professional writer could come up with something much better that that, but imagine Escape From Butcher Bay x Warriors x Aliens' third act.
The Riddick movies are just scifi wandering ronin flicks, a male power fantasy who fucks lethal aliens in the ass & makes them his jabronis. Those movies felt a bit 40K and Alien-inspired to me, like those worlds could exist as frontier systems in the AU.