Not sold on dumping the IG into that setting. Being far more ... formal Imperium in many ways ... the fiction really does seem to set the setting up to be more a tense western town. The SWA "gangs" are all choices that are "advance recon, away from command, scouting or exploring on the fringe" units. Except for Necrons, Tyranids, and IG.
Even the Space Marines and Tau are "behind the lines operatives," and a CSM team will quickly become predominantly human cultists. Heck, I even was convinced eventually by arguments regarding Harlequins [that they do go on "book retrieval missions" for the Black Library; and that they do disguise themselves as regular eldar, such as gardeners, yes, but then also potentially as pirates].
Tyranids can fill the "monster in the Sump" role, as a gang, I suppose.
But including the IG imports in a "military unit of full squad strength, acting as a branch of the military," which feels out of place as protagonists. Naval crews? There are other gangs that can represent that at least as well, if not better.
So what is a good argument in favour of including a line unit of Imperial Guardsmen aboard precipice, led by a sergeant?
Long before SWA, I started writing a campaign for classic Necromunda aboard a prison vessel that collided with a space hulk full or Orks and Genestealers. I never finished it, or played it, but I did end up renaming the territories like has been done here.
Dunno, got the dreaded ambull audio drama on audible and they come across a squad of fresh imp guard corpses in the Blackstone. Imperial insignia still visible. Their could be a connection between them and a rogue trader hired by a wacky magos biolo...whatevers made up latin.
Certainly the stories are ramping up to go cultist crazy.