Unfortunately we cannot add instancing support without the collaboration of the Octane developers. Recently we have included in RailClone an interface for rendering engines, and we sent the documentation to the main companies. So, hopefully new engines will be supported in the future, although until now we got no reply from Otoy.
It's strange the viewport error, because in Octane RailClone objects are handled as standard Max objects (which returns a mesh). We'll do more tests. This problem is not related with the Forest issue, because it works in a different way.
There are not special requirements regarding materials, multi-subs should work fine once converted to Octane. For this purpose, we include standard materials with the RailClone library, which are very suitable for the material converters.