I have implemented readObject to make loading objects from SceneLoader in the LWS plugin work. I'm not sure about other implications from changes leading up to this problem (readRefFile instead of readNodeFile in SceneLoader) but this fix works for me.

src/osgPlugins/lwo/ReaderWriterLWO.cpp

@@ -56,6 +56,11 @@ public:
 
     virtual const char* className() const { return "Lightwave Object Reader"; }
 
+    virtual ReadResult readObject(const std::string& file, const osgDB::ReaderWriter::Options* options) const
+    {
+      return readNode(file, options);
+    }
+
     virtual ReadResult readNode(const std::string& file, const osgDB::ReaderWriter::Options* options) const
     {
         std::string ext = osgDB::getLowerCaseFileExtension(file);