Could directionality be added independently here? I don't have an immediate use-case, but if this the current skeleton encodes structure of a graph, might as well add space allowing for directed graphs.

2D or 2+1D polygons? Like adding Shapely/GeoJSON compatibility would allow direct connection to 2+1D data models of tiled z-stacks. I can see Meshes being a link here, but they seem like overkill for something like 2D cell segmentation polygons in spatial transcriptomics

specifically list the types of objects somewhere in this section