Sense I saw the forged raiders and fact there hanging around a metal working factory made me think of the pit, which made me think they must be from there and slowly expanding. So thinking might have to go back there clear if the raiders were more well armed compared to other raiders, fuels for flamer throws fire bombs and much more.
So idea is the Pit got a hold of some plans the brother had for there airship, the raiders of the pit have metal working, machines and everything they could build one. So seeing raiders with a air ship of there own would be down right scary thought, so what ever group your with would try to stop them from finishing this ship or maybe take it for your own. There ship wouldn't be great like the brotherhoods is but still impressive feat none the least, drop fires bombs from the size and raids using maybe jet pack or papashoots (yes I know typo!) They be a force to not be taken lightly. Could have the dlc be on a timer for first part too get to the airship before it leaves/finished, if failed in getting there in time would leave and appear in the commonwealth and start wrecking the place, targeting the main threats to them first. Brotherhood, minutemen, gunners, and any raider or settler group who refuse to join them. You have to take it down a different way with each factions, minutemen blow it out of sky with mortors, railroad most like help minutemen, brother hood would either blow it away with prime or take it over for they can use it. Minutemen could take it over to I guess. But guess the DLC be called Forged Skies, Burning Skies, Raided Skies, Dreaded Skies, Stolen Skies.