This feature is already in our wishlist, but unfortunately animation support is more difficult than it seems at first glance.
For the instancing engine, an animated object is seen as different geometries (one for each time sample). So, to keep an optimal render performance, these geometries must be generated and handled properly before render starts.
Forest already does this process (using several mesh caches and other tricks), but RailClone not. In short, it can be done but requires important changes in the plugin core.