The proxies have some limitations for a plugin as RailClone, because they are not deformable (not bend or slice). This is the reason that currently the plugin use only pure meshes.
Anyways, we are working to provide VRay support to RailClone. It may be very useful for those scenes that don't require to deform the segments, as street lamps or along straight paths. The adaptation to VRay is fairly more complex than Forest, but you'll see some progress in the incoming beta release.