We added and tested reading of RLE-compressed segmentations, and did some experiments with writing, but I don’t recall if the result was documented. I think the main concern is that introducing compression will further complicate interoperability. Note that RLE would be applied after bit packing (for binary segmentations). Bit packing alone can be challenging for interoperability, and I am not convinced we should make it even more challenging.
No one asked about this before - it could be added as an option, but I would want to know how bit packing + RLE is supported in the existing tools before adding it.