Ebok: I agree very strongly with your principles of focusing on the interesting narrative that results from the consequences of a character's actions, yet the idea of making a Chopper go gangless for 3-5 sessions as they piece together a new gang as quickly as narratively possible... makes me a bit uncomfortable: to go smoothly, it'd require a patient player with the same mindset as us, unless it were done off-screen. I'm a bit reluctant to ask that of anyone. With the right player(s), I think it would work super well, and would be the ideal solution, for sure.
Absolutely! It depends entirely on the players, but as the MC--after a huge showdown that left strewn bodies all over, or after the uprising that overthrew the (possibly psychotic) leader of the pack/hardhold; it might be time for a few weeks of off-screen time while the characters lick their respective wounds. Loveletters! Provide the ways out of the crisis via options, stagger them with a stat or maybe just the 2d6+nothing to provide some measure of player agency in the choice, and then skip over to where he's got a few guys again, but...
Or that hardholder has rounded up some of his loyalists and retaken some supply routes, but...
Basically, if it looks like he'll be stranded without hope for multiple sessions and he doesn't think that's cool (some do), you don't have to give him a move to on scene take whatever just to fill the gap. The gap is real, it should *cost* him something to fake/replace/reclaim his standing. I think my largest reservation of your move was that it could be used regardless of circumstance to exponentially command everyone to be a fucking thieving hyena. This sounds more like Hocus territory, maybe even Hardholder territory (loosely) and absolutely nothing like a true chopper's recruiting methods. If you want an example in cinema of quick ways for a Boss to get a gang, look at Joker in Batman, or really any Mob movie, or if you're more sci-fy look at how liberate took power in continuum. Essentially: Find another gang, find another gangs leader, humiliate, butcher, murder, fucking end that guy, and look over the rest of the gang and say--Now you're mine. Then carrot stick, if you join me, we get THIS shiney promise. If you don't, well. *looks at post-leader* Your choice. That's sort'of both go aggro and manipulate, but it is a fast way to take power. (fast might not always come without strings or major complications, but those complications should be more subjective then just 1 hold fuck your other move).
small tangent: The above go aggro is certainly go aggro. the Promise just provides a narrative opportunity for those that say yes, to be happy about it. Giving in isn't always a with a grumble, its always with suspicion, but the specifics matter a lot more to the fallout then the dot-options in the move.
In general, you don't want to give automatic failures to their other rolls. Fucking thieves has its failures well covered, for example. Its not your job to have hold over their successes, its your job to make the hard moves when they're triggered. Any list of vulnerabilities aren't a one off checklist, they exist so long as the narrative says they do. And they trigger only when you need a new interesting hard-move and happen to pick that weakness. If you've got a murder in your gang that kills people for you happily, but also kills people whenever you don't send him to kill people, that can be story. It can have its own troubles, boons, and resolution without mechanics of any kind. Granted, if everything is dull and you gotta make a move, you can also lightly trigger some function of a weakness, just keep in mind how Hard (debilitating) that move should be.
example: Chopper raids a place, gets away with food, ammo, gas, and maybe some girls. Moral is high. Later when you need to make a move, you might say that one of your scouts is picking up radio chatter over the wastes, sounds like someone better armed is making their way towards them from the direction of settlement x. Thats a light move, using a new vulnerability created via their last action. Or maybe some time passes, and the Chopper is making a big move to attack another place--but some of guys have grown attached to the girls and they've been swayed againt the decision. Instead of just going sure boss, lets do it. They stand up and say, No--*reasons*. Pack Alpha time. A harder move might be, you fail a read a sitch when planning your next attack, and one of the girls got out and blew up your ammo/whatever and ran off. Or slit the throat of your second in command, or whatnot. What do you do? Push forward and let her go? your gang might question that. Ignore the target and go after the girl? Your gang might question that. Does the loss of ammo (or whatever) carry other vulnerabilities forward for the raid? Maybe for that fight, misses or tensions might be flavored around the loss. Who knows, but the point is that is all comes from the narrative as the essential trigger.
Or perhaps as a more on point
example: The Chopper decides to kamakazi his gang into a massive hardhold that is well stocked and prepared for him. Its been clearly stated this sounds like a bad idea but he forces their hand or kills some of his guys to make the rest go along with it. He strong believes he is invincible and that his Hard stats successes will carry his victory over *npc grudge*. He loses, but manages to survive. He's all alone, the only survivor outside like three others and two are captured and the third wants to kill him over this. Well shit, that's a hard place to be in for a Chopper. Maybe he gives up and heads out onto the roads, and we get a love letter of the few weeks or months later when some other opportunity arises or the past becomes relevant. Maybe he knows some drugged out wastelanders that slurp down this radioactive green tar and are sort of batshit crazy--he knows he can stir them up for his vengeance, but maybe it comes with the cost of (after he succeeds via go aggro-ing his way into power) he has to deal with radioactive mutant wasters and their (insane) off-kilter wants and desires. Those are real actions, with narrative cost. Its not your job to give him a move to ceed authority over to him about who is new gang, its your job to provide him opportunities in the narrative to make something better from nothing, even if he's just using these freaks as a temporary hold over before getting some normals back. (and leaving a rather pissed off or alternatively allied mutant raiders in the wastes) Maybe even when he leaves them behind, his reputation is stained by the common rumors that he was with those man-eaters and helped them kill people.
Maybe this, maybe that. There is really no end of the possibilities. Your move however... doesn't have the same range and isn't really needed either. If it were me, I'd probably throw in lots of small pockets of armed resistance for the chopper to manuever around during gameplay. If he lost, those pockets each become potential gangs. Maybe there are some scummy pirates that control a portion of the delta, or a thuggish family of farmers he's avoided thus far. The key is to make these possibilities many, and make thir respective cost make immediate narrative sense. What do the pirates want? Freedom, chaos, booty. What do the Family want? Consolidated control over their rivals. The Chopper can step into anywhere that has inactive violence and make it active violence simply by ceeding some of the flavor. At least up front.