Looking at the leaks for the Mont’ka campaign book, it appears that both Tau and the Astra Militarum are getting some ground-breaking new rules, including detachments, formations, WL traits, and Relics.
From an Astra Militarum perspective, the formation that jumps out to me immediately is the Emperor’s Wrath Artillery Company:
-1 x Company Command Squad (must take Chimera or Taurox)
-2 x Basilisk/Wyvern/Hydra Batteries, in any combination
-1 x Manticore or Deathstrike
In terms of Special Rules, the formation allows the Company Commander to issue orders to vehicles from this formation, specifically the Smite at Will (unit gains Split Fire), Suppressive Fire (unit gains Pinning for its shooting), and Fire on My Target (Units gains Ignore Cover for its shooting), as long as they pass a Ld check on roll of 8 or less. Additionally, if the Company Command Squad has a Vox Caster, then the Guardsman with the Vox Caster can pick one enemy within 18″ and LOS to become a “target,” which causes all the rest of the units to become Twin-Linked when shooting at that specific “target” for the rest of the turn.
As you can tell, these rules are Extremely powerful, making already good units top-tier competitors in almost any game. In particular, the ability to give Basilisks, Hydras, and Manticores “Ignore Cover” is a game-changer (Wyverns and Deathstrikes already ignore cover with their shooting).
Imagine two Batteries of 2 x Basilisks each, with a nearby Company Command Squad (and a pair of attached Enginseers) “casting” Fire on My Target on both of them successfully. That is 4 x S9 AP3 Ordnance, Large Blast, Ignore Cover shots per shooting phase, which can threaten almost any unit in the game (except Flyers and FMCs). Additionally, the two Enginseers can use their Awaken the Machine ability to give two of the Basilisks Power of the Machine Spirit, essentially giving them “free” Split Fire, so you can target up to four different enemy units with this shooting. Finally, the Enginseers can repair vehicles that have lost HPs or have Weapons Destroyed/Immobilized results, making this battle group more durable in the long-run. All of this firepower can be further supplemented by the Manticore from this formation, a Master of Ordnance attached to the Command Squad and shooting his own “one-man Basilisk shot,” and a Vox Caster Veteran who can “spot” for more accurate shooting by the Artillery.
The beauty of this formation is that it is not only available to Astra Militarum armies in the Cadian Battle Group special detachment, but since it is its own formation, any Imperium army can take it as a Battle Brother.
I know numerous armies that would love to access to this kind of long-range, Large Blast, Ignore Cover fire support, including but not limited to:
-Sisters of Battle
Even Allies of Convenience, like Eldar and Harlequins, would still find the Emperor’s Wrath Artillery Company an excellent “firebase” ally, especially Harlequins, to supplement their own mobility, shooting, and close combat capabilities.