Helldivers 2's developers have considered adding underground maps, though we wouldn't hold our breath waiting for it to happen as it would require a huge commitment, and it'd likely be "friendly fire hell" anyway.
In the game's official Discord server, one Arrowhead Game Studios community manager was asked if there would be "some cave underground maps" at some point in the future of Helldivers 2. The asker wondered if there was a place for "close corridor" fighting against swarms of enemies, including Automatons, and "close quarter combat" against foes.
A community member responded that while they "don't know" if underground maps are in the future of Helldivers 2, it was something that Arrowhead "contemplated" at one point. "And yes they could be really cool, but they would also require a lot of tech and logistics based on it being a very different kind of gameplay wise than surface fighting," the community manager added.
The developer points to two obvious issues with underground maps: a lack of Stratagems, which descend from Super Destroyers in the atmosphere, and "friendly fire hell" in close-quarters, corridor-based gameplay. I think it's pretty safe to say that a lot of Super Earth's finest would get gunned down by their own comrades in close quarters, especially in relatively narrow corridors.
Elsewhere the Helldivers 2 Democratic Detonation Warbond just launched today, containing brand new weapons, armor, and cosmetic items as per usual. Alongside the Warbond though, there's a new ship module update adding four of the most expensive upgrades in all of Helldivers 2, which I'll inevitably be grinding months for.
