Muskets have already been added, along with flintlocks and other black powder weapons, but there is nothing at all bridging the gap between the 1400s and the 1800s in Rimworld.

The framework is there; we have muskets and the like at the end of the medieval tech level. Slap in some cannons as re-skinned mortars and maybe a few new swords and apparel types and you're pretty much set.

Could even create a pirates faction that has a coastal raid type and spawns boats with cannons at the edge of the map as a siege if you want something extra special.