Unity: Un attributo para usar en strings, te lo muestra como selector de Asset de Escenas en el Inspector, (pero escribe el path a al escena o el nombre de la escena). ¡Funciona con Arrays!

SceneAssetPathAsStringAttributeDrawer.cs

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
#if UNITY_EDITOR
using UnityEditor;
#endif

public class SceneAssetPathAsStringAttribute : PropertyAttribute
{
    readonly bool incluirTodoElPath;

    public SceneAssetPathAsStringAttribute() : this(false) { }
    public SceneAssetPathAsStringAttribute(bool incluirTodoElPath)
    {
        this.incluirTodoElPath = incluirTodoElPath;
    }

#if UNITY_EDITOR
    [CustomPropertyDrawer(typeof(SceneAssetPathAsStringAttribute))]
    public class SceneAssetPathAsStringAttributeDrawer : PropertyDrawer
    {
        public override void OnGUI(Rect position, SerializedProperty property, GUIContent label)
        {
            if (property.propertyType != SerializedPropertyType.String)
            {
                EditorGUI.HelpBox(position, "Solo usar con strings", MessageType.Error);
                return;
            }

            var scene = AssetDatabase.LoadAssetAtPath<SceneAsset>(property.stringValue);
            if (scene == null && !string.IsNullOrEmpty(property.stringValue))
            {
                string[] guids = AssetDatabase.FindAssets(property.stringValue + " t:scene");
                if (guids.Length > 0) scene = AssetDatabase.LoadAssetAtPath<SceneAsset>(AssetDatabase.GUIDToAssetPath(guids[0]));
            }

            EditorGUI.BeginChangeCheck();
            scene = EditorGUI.ObjectField(position, label, scene, typeof(SceneAsset), false) as SceneAsset;
            if (EditorGUI.EndChangeCheck())
            {
                var att = attribute as SceneAssetPathAsStringAttribute;
                if (att.incluirTodoElPath)
                {
                    property.stringValue = AssetDatabase.GetAssetPath(scene);
                }
                else
                {
                    property.stringValue = scene.name;
                }
            }
        }
    }
#endif
}