New component: SceneGraph, lets you create a graph inside the scene which can reference scene objects.

Examples.meta

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Scripts/Editor/SceneGraphEditor.cs

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+using System;
+using System.Collections;
+using System.Collections.Generic;
+using UnityEditor;
+using UnityEngine;
+using XNode;
+
+namespace XNodeEditor {
+    [CustomEditor(typeof(SceneGraph), true)]
+    public class SceneGraphEditor : Editor {
+        private SceneGraph sceneGraph;
+        private bool removeSafely;
+        private Type graphType;
+
+        public override void OnInspectorGUI() {
+            if (sceneGraph.graph == null) {
+                if (GUILayout.Button("New graph", GUILayout.Height(40))) {
+                    if (graphType == null) {
+                        Type[] graphTypes = NodeEditorReflection.GetDerivedTypes(typeof(NodeGraph));
+                        GenericMenu menu = new GenericMenu();
+                        for (int i = 0; i < graphTypes.Length; i++) {
+                            Type graphType = graphTypes[i];
+                            menu.AddItem(new GUIContent(graphType.Name), false, () => CreateGraph(graphType));
+                        }
+                        menu.ShowAsContext();
+                    } else {
+                        CreateGraph(graphType);
+                    }
+                }
+            } else {
+                if (GUILayout.Button("Open graph", GUILayout.Height(40))) {
+                    NodeEditorWindow.Open(sceneGraph.graph);
+                }
+                if (removeSafely) {
+                    GUILayout.BeginHorizontal();
+                    GUILayout.Label("Really remove graph?");
+                    GUI.color = new Color(1, 0.8f, 0.8f);
+                    if (GUILayout.Button("Remove")) {
+                        removeSafely = false;
+                        sceneGraph.graph = null;
+                    }
+                    GUI.color = Color.white;
+                    if (GUILayout.Button("Cancel")) {
+                        removeSafely = false;
+                    }
+                    GUILayout.EndHorizontal();
+                } else {
+                    GUI.color = new Color(1, 0.8f, 0.8f);
+                    if (GUILayout.Button("Remove graph")) {
+                        removeSafely = true;
+                    }
+                    GUI.color = Color.white;
+                }
+            }
+        }
+
+        private void OnEnable() {
+            sceneGraph = target as SceneGraph;
+            Type sceneGraphType = sceneGraph.GetType();
+            if (sceneGraphType == typeof(SceneGraph)) {
+                graphType = null;
+            } else {
+                Type baseType = sceneGraphType.BaseType;
+                if (baseType.IsGenericType) {
+                    graphType = sceneGraphType = baseType.GetGenericArguments() [0];
+                }
+            }
+        }
+
+        public void CreateGraph(Type type) {
+            serializedObject.Update();
+            sceneGraph.graph = ScriptableObject.CreateInstance(type) as NodeGraph;
+            serializedObject.ApplyModifiedProperties();
+        }
+    }
+}

Scripts/Editor/SceneGraphEditor.cs.meta

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Scripts/SceneGraph.cs

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+using System.Collections;
+using System.Collections.Generic;
+using UnityEngine;
+using XNode;
+
+namespace XNode {
+	/// <summary> Lets you instantiate a node graph in the scene. This allows you to reference in-scene objects. </summary>
+	public class SceneGraph : MonoBehaviour {
+		public NodeGraph graph;
+	}
+
+	/// <summary> Derive from this class to create a SceneGraph with a specific graph type. </summary>
+	/// <example>
+	/// <code>
+	/// public class MySceneGraph : SceneGraph<MyGraph> {
+	/// 	
+	/// }
+	/// </code>
+	/// </example>
+	public class SceneGraph<T> : SceneGraph where T : NodeGraph {
+		public new T graph { get { return base.graph as T; } set { base.graph = value; } }
+	}
+}

Scripts/SceneGraph.cs.meta

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