So, it appears we have leaked rules for Shadowstrike Kill Team (i.e. the new Raven Guard Formation):
Looking over these, this formation has 2-4 Scout Squads and 1-3 Vanguard Vet squads. With those units, the formation gets the following special rules:
1 – Can choose to automatically fail or pass reserve rolls for Vanguard Vets
2 – Vanguard Vets do not scatter if they DS within 9″ of one of the Scout squads
3 – Vanguard Vets can charge the same turn they DS
Combine this with RG Chapter Tactics (i.e. Shrouded Scouts turn 1, which can be combined with Camo Cloaks and regular terrain for an automatic 2+ cover save; Jump Packs able to be used in both Movement and Assault for Vanguard Vets) and you have a very decent little formation here.
I think the best way this can be employed is to kit the Vanguard Vets out as “Monster Hunters” (i.e. PF, SS, and JP for all models) and then use the Scouts to bring them in turn 2 automatically with no scatter and charge an enemy “uber” unit of their choice, be it Eldar Wraithknight, Tau Ta’unar Lord of War, AM Leman Russ Squadron, Grav Centurion Deathstar, Imperial Knight, Necron Phalanx, Orky Battlewagon Brigade, Nid Hive Tyrant, or CSM Nurgle Obliterators.
Just for an example, imagine a 10 man VV squad charging an Eldar Wraithknight (with Prescience cast on them from a nearby Librarian). WK strikes first with 4A base, causing 0-1 unsaved wounds on average against the SS equipped VVs. With 9 VVs left, that means they strike back with 27 attacks, 20-21 hits, 10-11 wounds, and 6-7 unsaved wounds after the Wraithknight gets its FNP rolls (i.e. the Wraithknight is dead)… the VV still have to absorb any Stomp hits, but with good spacing and use of their Storm Shields, they should be able to economically absorb these hits (especially in exchange for killing the Wraithknight).
Take the same Vanguard Vet squad and have them multi-charge several enemy Leman Russ tanks (remember, no penalty for Multi-charging because of Heroic Intervention rule)… even with AV11 rear armor on the tougher Leman Russ variants, the squad should get 30 attacks, 26-27 hits (with Prescience), and 17-18 glancing hits (or better), meaning that they can easily wipe out an entire squadron of Leman Russes without breaking a sweat. Same logic can be applied to mass Ork Battlewagons (i.e. from the Blitz Brigade formation), except with even better results, since Battlewagons have AV10 rear armor and are open-topped.
Against an enemy Centurion Deathstar with 6 x Grav Centurions and Invisibility cast on it, this same squad gets 30 attacks, about 9-10 hits (6+s to Hit due to Invisibility, with re-rolls from Prescience), and about 8 unsaved wounds (or 4 dead Centurions), which is more than enough to cripple the Deathstar for the rest of the game. Finally, against an Imperial Knight this squad generates 30 attacks, 22-23 hits, and 7-8 glancing hits on average, which translates into one 400 point Imperial Knight destroyed.
However you slice it, I think this formation is going to be a winner, particularly if used in a role as a designated “titan killer” type unit that is equipped and deployed to destroy enemy super units.