exclusive to necromunda. though no doubt the minis will work in 40k as cultists.
It was in GWs presentation of what they've got planned for necromunda at adetpicon i think it was. They listed all the upcoming factions and "chaos uprising" was one in addition to the WD "chaos cultists" we just got. Chaos uprising was put with guilds and enforcers so we can reasonably assume that means getting dedicated minis and rules in a gang war book.