Custom co-ordinate systems are supported across many of the Bentley tools.
Custom co-ord systems can be developed in MicroStation and applied to iTwin Capture Modeler data sets (reality meshes) and to iTwin imodels.
Support for assignment of the same custom co-ordinate system is required to ensure streaming PointClouds (OPC) can be used in both MicroStation and iTwin imodel context.
Because OPC doesn't support local geoids there are offset between model and point cloud. Both produced from same reference model but there are height differences. Why geoids are such an issue for most of the softwares I do not get it. Just calculate the offset and write it for local file in metadata there is no need to have geoid for whole country to display one model.