One of the most popular D&D settings is Spelljammer, a supplement that turns your sword & sorcery to space-faring swashbuckling. While it's certainly a tone shift, it's not an unreasonable one—fantasy adventuring and the idea of a great, unexplored frontier have a lot to do with space. Treasure Planet understood this, as does Pathfinder 2e, which also has Starfinder as another setting.
If you're John Harper, creator of TTRPG darling Blades in the Dark, or Tim Denee, tasked with writing a supplement to said system, you might be wondering how to make a similar statement with a setting overhaul—especially since BoTD's setting is so very specific. In case you're unfamiliar, most BoTD games take place in Duskvol, which is a post-apocalyptic gothic city surrounded by a blood sea and walls of lightning to keep the ghouls and spectres out. Inside that city, you do crimes.
