Space marines of the 41st millenium
I'm gonna try a different tack with this game, assuming it ever happens: I'm gonna lay out the plan ahead of time, so that everyone knows what the game is about, instead of challenging the players to discover that on their own.
Contents
The Big Idea
The idea here is that the bulk of the players are Space Marines: roided out, superhuman killing machines, one unit of a few that are stranded on a bombed-out hive-world colony, trying to preserve the people that are left, and fight off an alien menace, and at the same time try to preserve what society is left on the planet. Likely the planet will have its secrets, as well...
I'd probably set this game in the WH40k universe, on a planet stuck in the Maelstrom, so the players would be from one of the chapters of marines that's more like grizzled special forces, and less like fanatical crusaders.
The central core of the game wouldn't be combat, though it'd happen. It'd be the fact that the players are highly trained killers, but their relative power makes them the defacto leaders of the planet. Sure, a Navy SEAL is great at killing the hell out of people - is he so great at talking down the family of someone killed in the crossfire? Is he good at ensuring the peace? Can he keep a society stable without going native?
The Rules
I've decided that for a one-shot, I'm gonna change this up to use the DitV system.
The idea is the same; the players are Marines, sent to a planet for a reason of some kind, and have to lead/inspire/browbeat/kill the regular people on that planet.
I see large-scale squad-style fights involved, with each player leading some number of other NPCs in battle.
Space Marines in the Vineyard
Marines work better for the DitV system than a lot of other options, I think; they have a command structure, and a nominal mission, so they generally have an incentive to get involved in a situation for better or worse.
Special rules would be as follows: a Space Marine automatically gets a 'super' trait, rated at d20 (oh so nerdy), called "Space Marine". If the player can make a good argument to fellow players and the GM that a Space Marine would be better in this given situation, he can roll it - it's just that when using it in raises, the player needs to have a suitably outsize description of what happens, like "I spit my Space Marine acid in his face, knee him in the groin, and pin him on the ground." You can't roll your Space Marine die unless it's a suitably dramatic action.
Dramatic Large Battle System
Since a fair amount of SMitV would revolve around leading troops into battle, I've innovated the Dynamic Large Battles in the Vineyard (DLBitV) system. Mechanically, it's similar to the standard conflict resolution in DitV.
Types
Battle is broken up into types: Parley, Long-range, and Close. The Stats rolled for the various stages of battle are different though - Heart + Acuity for Parley, Acuity + Will for Long-range, and Body + Will for close range.
Each is a specific conflict, and the winner of an early phase takes bonus dice to the next phase. Any unused dice from an early phase may also be carried over into the next.
Giving in a phase means termination of the entire conflict and that fallout up to that point is calculated. A Commander can't Give in the Parley phase and then initiate Long or Short range conflict - a phase must be played completely through, until one side has no dice left.
Commander
The Commander of a force will always be a PC Space Marine, or an Important NPC. They use their same Traits, whichever applicable for the current phase of combat. Note that two PC Space Marines cannot join into one force, and that a force composed only of a PC Space Marine or NPC is completely viable.
Soldiers
Solders are rated in dice, added as Traits to the Commander's Traits, and rolled at the time they're brought into play. Raises using soldier dice must account for the actions those soldiers take. For instance, if your Force had "Veteran Scouts 2d8", and you committed them during the Parley phase, you'd roll the dice then, and probably do some raises against the information your scouts collected.
Miniatures
Ideally, the battle is played out with miniatures, on a tabletop space. Every raise involves moving some of these miniatures around; if the raise is the Commander's and a general tactical maneuver, the Commander can move any of his models; if it's only from Forces dice, then only the Forces whose dice are involved in the raise may move.
Fallout
Fallout isn't calculated until after the battle(?). Dice of Fallout cancel out dice of Forces or act normally on the Commander, at the Commander's discretion.
The Setting
The setting would be a world in the Maelstrom, so cut off from the Imperium at large. Furthermore, they'd be crash-landed on a planet with no real hope of escape. I think the Marines in question would be Astral Claws, the chapter of Huron Blackheart, famous renegade, though the story from his side of things is a little different.
Since the players are stranded, equipment would be limited. To represent this without it becoming the focus of the game, I think I'd allow a certain amount of equipment use per session more or less without penalty, but extended use (say full-auto bolter spray, or several armor-penetrating hits) incurs a penalty to future freedom of equipment use.
