Physical_structures API

Preview/ghost structure before spawning (semi-transparent client-side rendering) for UX
Nested/composite structures (multiple NBT files as a single "set" with relative offsets) for large structures (ships, bases). 
Loading NBT via absolute path/from other mods — currently, getResourceOrThrow requires the NBT to be located in the mod’s resources; it would be worth adding a PhysicalStructureDefinition variant that supports an arbitrary ResourceLocation from a third-party namespace without needing to copy the file, or a loader from the player’s config//datapack folder
Configurable assembly
Dynamic registration at runtime via API (PhysicalStructures.registerStructure(def) without JSON and without a restart)
There is also support for the .excraft format from the create_aeronautics_toolgun mod