.../Core/Plugin/PluginWithHandlersInterface.php    | 42 +++++++++++++++++
 .../Drupal/Core/Plugin/PluginWithHandlersTrait.php | 53 ++++++++++++++++++++++
 core/modules/media/src/MediaStorageProxyBase.php   |  2 +-
 .../MediaStorageProxyMetadataHandlerInterface.php  |  2 +-
 core/modules/media/src/MediaTypeForm.php           |  4 +-
 .../src/Plugin/MediaStorageProxy/Test.php          | 30 ++++++------
 .../MediaStorageProxy/TestMetadataHandler.php      | 40 ++++++++++++++++
 7 files changed, 152 insertions(+), 21 deletions(-)

diff --git a/core/lib/Drupal/Core/Plugin/PluginWithHandlersInterface.php b/core/lib/Drupal/Core/Plugin/PluginWithHandlersInterface.php
new file mode 100644
index 0000000..3564713
--- /dev/null
+++ b/core/lib/Drupal/Core/Plugin/PluginWithHandlersInterface.php
@@ -0,0 +1,42 @@
+<?php
+
+namespace Drupal\Core\Plugin;
+
+use Drupal\Component\Plugin\PluginInspectionInterface;
+
+/**
+ * Provides an interface for plugins which have handlers.
+ *
+ * Plugin handlers are embeddable handlers referenced by the plugin annotation.
+ * Used by plugin types which have lots of responsibilities, with particular
+ * categories.
+ */
+interface PluginWithHandlersInterface extends PluginInspectionInterface {
+
+  /**
+   * Determines if there is a handler for a given type.
+   *
+   * @param string $handler_type
+   *   The type of handler to check.
+   * @param bool $nested
+   *   (optional) If this handler has a nested definition. Defaults to FALSE.
+   *
+   * @return bool
+   *   TRUE if a handler of this type exists, FALSE otherwise.
+   */
+  public function hasHandlerClass($handler_type, $nested = FALSE);
+
+  /**
+   * @param string $handler_type
+   *   The handler type to get.
+   * @param bool $nested
+   *   (optional) If this handler has a nested definition. Defaults to FALSE.
+   *
+   * @return array|string|null
+   *   The handlers for a given type, or NULL if none exist.
+   */
+  public function getHandlerClass($handler_type);
+
+  public function getHandler($handler_type, $nested = FALSE);
+
+}
diff --git a/core/lib/Drupal/Core/Plugin/PluginWithHandlersTrait.php b/core/lib/Drupal/Core/Plugin/PluginWithHandlersTrait.php
new file mode 100644
index 0000000..a25b6e9
--- /dev/null
+++ b/core/lib/Drupal/Core/Plugin/PluginWithHandlersTrait.php
@@ -0,0 +1,53 @@
+<?php
+
+namespace Drupal\Core\Plugin;
+
+/**
+ * Provides a trait with typical behavior for plugins which have handlers.
+ *
+ * @see \Drupal\Core\Plugin\PluginWithHandlersInterface
+ */
+trait PluginWithHandlersTrait {
+
+  // MUST BE IMPLEMENTED NOT BY THE TRAIT BUT BY THE PLUGIN USING THIS TRAIT
+  // … I don't know how to document this correctly.
+//  protected function getInterfacesForHandlerTypes() {
+//    return [
+//      'metadata' => 'classname',
+//    ];
+//  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getHandlerClass($handler_type, $nested = FALSE) {
+    $handlers_annotation = $this->getPluginDefinition()['handlers'];
+    if (isset($handlers_annotation[$handler_type]) && (!$nested || isset($handlers_annotation[$handler_type][$nested]))) {
+      return $nested ? $handlers_annotation[$handler_type][$nested] : $handlers_annotation[$handler_type];
+    }
+    // Allow plugins to opt in to be their own handler of this type.
+    $interface = $this->getInterfacesForHandlerTypes()[$handler_type];
+    if ($this instanceof $interface) {
+      return static::class;
+    }
+    return FALSE;
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function hasHandlerClass($handler_type, $nested = FALSE) {
+    return !empty($this->getHandlerClass($handler_type, $nested));
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getHandler($handler_type, $nested = FALSE) {
+    $class = $this->getHandlerClass($handler_type, $nested);
+    // @todo always inject context (at minimum source field configuration), see EntityHandlerInterface
+    // @todo allow handlers to use dependency injection from the container, see ContainerInjectionInterface
+    return new $class();
+  }
+
+}
diff --git a/core/modules/media/src/MediaStorageProxyBase.php b/core/modules/media/src/MediaStorageProxyBase.php
index 69e90a3..46bb095 100644
--- a/core/modules/media/src/MediaStorageProxyBase.php
+++ b/core/modules/media/src/MediaStorageProxyBase.php
@@ -15,7 +15,7 @@
 /**
  * Base implementation of media storage proxy plugin.
  */
-abstract class MediaStorageProxyBase extends PluginBase implements MediaStorageProxyInterface, MediaStorageProxyMetadataHandlerInterface, MediaStorageProxyThumbnailHandlerInterface, ContainerFactoryPluginInterface {
+abstract class MediaStorageProxyBase extends PluginBase implements MediaStorageProxyInterface, MediaStorageProxyThumbnailHandlerInterface, ContainerFactoryPluginInterface {
 
   /**
    * Plugin label.
diff --git a/core/modules/media/src/MediaStorageProxyMetadataHandlerInterface.php b/core/modules/media/src/MediaStorageProxyMetadataHandlerInterface.php
index ba31414..d84c8c8 100644
--- a/core/modules/media/src/MediaStorageProxyMetadataHandlerInterface.php
+++ b/core/modules/media/src/MediaStorageProxyMetadataHandlerInterface.php
@@ -30,7 +30,7 @@
  *
  * @see \Drupal\media\MediaStorageProxyInterface
  */
-interface MediaStorageProxyMetadataHandlerInterface extends MediaStorageProxyInterface {
+interface MediaStorageProxyMetadataHandlerInterface {
 
   /**
    * Provide a default name for the media item.
diff --git a/core/modules/media/src/MediaTypeForm.php b/core/modules/media/src/MediaTypeForm.php
index 2b774a6..158391a 100644
--- a/core/modules/media/src/MediaTypeForm.php
+++ b/core/modules/media/src/MediaTypeForm.php
@@ -151,7 +151,7 @@ public function form(array $form, FormStateInterface $form_state) {
       ],
     ];
 
-    if (empty($handler) || empty($handler->getMetadataLabels())) {
+    if (empty($handler) || empty($handler->getHandler('metadata')->getMetadataLabels())) {
       $form['handler_dependent']['field_map']['#access'] = FALSE;
     }
     else {
@@ -163,7 +163,7 @@ public function form(array $form, FormStateInterface $form_state) {
       }
 
       $field_map = $this->entity->getFieldMap();
-      foreach ($handler->getMetadataLabels() as $metadata_attribute_name => $metadata_attribute_label) {
+      foreach ($handler->getHandler('metadata')->getMetadataLabels() as $metadata_attribute_name => $metadata_attribute_label) {
         $form['handler_dependent']['field_map'][$metadata_attribute_name] = [
           '#type' => 'select',
           '#title' => $metadata_attribute_label,
diff --git a/core/modules/media/tests/modules/media_test_handler/src/Plugin/MediaStorageProxy/Test.php b/core/modules/media/tests/modules/media_test_handler/src/Plugin/MediaStorageProxy/Test.php
index d06bf95..20ce372 100644
--- a/core/modules/media/tests/modules/media_test_handler/src/Plugin/MediaStorageProxy/Test.php
+++ b/core/modules/media/tests/modules/media_test_handler/src/Plugin/MediaStorageProxy/Test.php
@@ -3,8 +3,10 @@
 namespace Drupal\media_test_handler\Plugin\MediaStorageProxy;
 
 use Drupal\Core\Form\FormStateInterface;
+use Drupal\Core\Plugin\PluginWithHandlersTrait;
 use Drupal\media\MediaInterface;
 use Drupal\media\MediaStorageProxyBase;
+use Drupal\media\MediaStorageProxyMetadataHandlerInterface;
 use Drupal\media\MediaTypeInterface;
 
 /**
@@ -15,10 +17,21 @@
  *   label = @Translation("Test media storage proxy"),
  *   description = @Translation("Media storage proxy for testing purposes."),
  *   allowed_field_types = {"string"},
+ *   handlers = {
+ *     "metadata" = "Drupal\media_test_handler\Plugin\MediaStorageProxy\TestMetadataHandler",
+ *   }
  * )
  */
 class Test extends MediaStorageProxyBase {
 
+  use PluginWithHandlersTrait;
+
+  protected function getInterfacesForHandlerTypes() {
+    return [
+      'metadata' => MediaStorageProxyMetadataHandlerInterface::class,
+    ];
+  }
+
   /**
    * {@inheritdoc}
    */
@@ -36,23 +49,6 @@ public function getThumbnail(MediaInterface $media) {
   /**
    * {@inheritdoc}
    */
-  public function getMetadataLabels() {
-    return [
-      'attribute_1' => $this->t('Attribute 1'),
-      'attribute_2' => $this->t('Attribute 2'),
-    ];
-  }
-
-  /**
-   * {@inheritdoc}
-   */
-  public function getMetadata(MediaInterface $media, $attribute_name) {
-    return FALSE;
-  }
-
-  /**
-   * {@inheritdoc}
-   */
   public function defaultConfiguration() {
     return parent::defaultConfiguration() + [
       'test_config_value' => 'This is default value.',
diff --git a/core/modules/media/tests/modules/media_test_handler/src/Plugin/MediaStorageProxy/TestMetadataHandler.php b/core/modules/media/tests/modules/media_test_handler/src/Plugin/MediaStorageProxy/TestMetadataHandler.php
new file mode 100644
index 0000000..32837bc
--- /dev/null
+++ b/core/modules/media/tests/modules/media_test_handler/src/Plugin/MediaStorageProxy/TestMetadataHandler.php
@@ -0,0 +1,40 @@
+<?php
+
+namespace Drupal\media_test_handler\Plugin\MediaStorageProxy;
+
+use Drupal\Core\StringTranslation\StringTranslationTrait;
+use Drupal\media\MediaInterface;
+use Drupal\media\MediaStorageProxyMetadataHandlerInterface;
+
+/**
+ * @see \Drupal\media_test_handler\Plugin\MediaStorageProxy\Test
+ */
+class TestMetadataHandler implements MediaStorageProxyMetadataHandlerInterface  {
+
+  use StringTranslationTrait;
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getDefaultName(MediaInterface $media) {
+    return 'Test';
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getMetadataLabels() {
+    return [
+      'attribute_1' => $this->t('Attribute 1'),
+      'attribute_2' => $this->t('Attribute 2'),
+    ];
+  }
+
+  /**
+   * {@inheritdoc}
+   */
+  public function getMetadata(MediaInterface $media, $attribute_name) {
+    return FALSE;
+  }
+
+}