Sort of a necro, but if there's still any interest in this, I think I could do it pretty easily. I've got a good base for firearms and emplaced machine guns from Underhive Settlement and I think I can imagine how this might work - no farming (unless there's any precedent that states otherwise. or if no farming proves unfun), soil-only digging. During one season, caravans bring supply crates full of rifles, machine guns, uniforms and ammunition with a negative cost, blocks of concrete for bunkers, packs of cigarettes, water and food. During all the rest you're swamped with invaders. Wood would be your primary building material. Rather than child immigrants, you get wounded soldiers that "grow up" in a year at most. (Actually, is it possible to make a race be born as adults? There wouldn't be in-game reproduction, at any rate.) Might have to fiddle with emotions, too. Tantrum spirals may not be suited to a trench warfare setting.
I see it looking sorta like Kobold Camp but with a lot more gun violence. And trench clubs.
Also, should there be human soldiers or just dorfs, goblins, etc updated to a WWI-ish setting? I'm leaning strongly for the latter.