The latest Decurion Detachment for Necrons that has just been revealed this week, is shedding light on what may very quickly become a way for Games Workshop to specialize armies to fit into a quick narrative. While codex supplements were doing this in a bigger way, with new warlord traits and artifacts, this way of quickly restructuring a codex's forces into specialized detachments, may become a very regular occurrence.
Please remember that this is a rumor.
via TKoS on Faeit 212
The decurion detachment will not be a Necron only thing. The standard FOC
was designed with the Space Marine company structure in mind, and GW has
been toying around with new ways to building fluffy armies. Looking back
the Archangel Strikeforce from Shield of Ball, this can can be seen as a
prototype for a decurion detachment.
IG will be getting their own decurion in a dataslate some time in the
future, and the Necron force from IA12 will be getting one as well. Expect
2-6 warriors, 1-6 flayed ones, and 1-3 charnel scarabs, but this is just
Expect more decuron formations to pop up in expansions and future codex
updates, but don't think FOC charts are going away. Decurion formations
will become the new "fluffy" lists; options that more closely adhere to the
quirks and idiosyncrasies of specific Warlords or factions.