Scriptablable object as protobuf message container

ItemCatalog.cs

using UnityEngine;
using io.gamemachine.messages;

namespace GameMachine {
    namespace ItemManagement {

        [CreateAssetMenu(menuName =@"ItemCatalog")]
        public class ItemCatalog : ScriptableProtobuf<PlayerItems> {
        }
    }
}

Messages.proto

message PlayerItem {
...
}

message PlayerItems {
  repeated PlayerItem playerItems = 1;
}

ScriptableProtobuf.cs

using UnityEngine;
using System.IO;
using ProtoBuf;
using System;

namespace GameMachine {
    public class ScriptableProtobuf<T> : ScriptableObject where T :IExtensible  {

        public static string dataDirectory = System.IO.Path.GetFullPath(Application.dataPath + "/protobuf_data");
        public static string fileExtension = ".pb";

        public string id;
        private T data;
        private bool loaded = false;

        public T GetData() {
            if (!loaded) {
                Load();
            }
            return data;
        }

        public void Save() {
            MemoryStream stream = new MemoryStream();
            Serializer.Serialize(stream, data);
            System.IO.File.WriteAllBytes(DataFilePath(), stream.ToArray());
            loaded = false;
        }

        public T Clone(T data) {
            MemoryStream stream = new MemoryStream();
            Serializer.Serialize(stream, data);

            stream = new MemoryStream(stream.ToArray());
            return Serializer.Deserialize<T>(stream);
        }

        public void Import(byte[] bytes) {
            System.IO.File.WriteAllBytes(DataFilePath(), bytes);
            loaded = false;
        }

        private void EnsurePath() {
            if (!System.IO.Directory.Exists(dataDirectory)) {
                System.IO.Directory.CreateDirectory(dataDirectory);
            }
        }
        
        private string DataFilePath() {
            if (string.IsNullOrEmpty(id)) {
                id = Guid.NewGuid().ToString();
            }
            return dataDirectory + "/" + this.GetType().Name+"_"+id + fileExtension;
        }

        private bool DataFileExists() {
            return (File.Exists(DataFilePath()));
        }

        private void Load() {
            if (!loaded) {
                EnsurePath();
                if (!DataFileExists()) {
                    data = Activator.CreateInstance<T>();
                } else {
                    byte[] bytes = System.IO.File.ReadAllBytes(DataFilePath());
                    MemoryStream stream = new MemoryStream(bytes);
                    data = Serializer.Deserialize<T>(stream);
                }
            }
        }
    }
}