interdiff impossible; taking evasive action
reverted:
--- b/core/modules/field/field.module
+++ a/core/modules/field/field.module
@@ -6,8 +6,6 @@
  */
 
 use Drupal\Core\Config\ConfigImporter;
-use Drupal\Core\Entity\Entity\EntityFormDisplay;
-use Drupal\Core\Entity\Entity\EntityViewDisplay;
 use Drupal\Core\Entity\EntityTypeInterface;
 use Drupal\Core\Entity\DynamicallyFieldableEntityStorageInterface;
 use Drupal\field\ConfigImporterFieldPurger;
@@ -349,47 +347,6 @@
   }
 }
 
-/**
- * Implements hook_ENTITY_TYPE_insert() for 'field_config'.
- *
- * Allow other view modes to update their configuration for the new field.
- * Otherwise, configuration for view modes won't get updated until the mode
- * is used for the first time, creating noise in config diffs.
- *
- * @see https://www.drupal.org/node/2915036
- */
-function field_field_config_insert(FieldConfigInterface $field) {
-  if ($field->isSyncing()) {
-    // Don't change anything during a configuration sync.
-    return;
-  }
-
-  $entity_type_id = $field->getTargetEntityTypeId();
-  $bundle = $field->getTargetBundle();
-
-  $entity_display_repository = \Drupal::service('entity_display.repository');
-  $view_modes = $entity_display_repository->getViewModes($entity_type_id);
-  $form_modes = $entity_display_repository->getFormModes($entity_type_id);
-
-  // Update view modes.
-  foreach ($view_modes as $view_mode_id => $view_mode) {
-    if ($view_mode['status']) {
-      if ($display = EntityViewDisplay::load($entity_type_id . '.' . $bundle . '.' . $view_mode_id)) {
-        $display->save();
-      }
-    }
-  }
-
-  // Update form modes.
-  foreach ($form_modes as $form_mode_id => $form_mode) {
-    if ($form_mode['status']) {
-      if ($form_display = EntityFormDisplay::load($entity_type_id . '.' . $bundle . '.' . $form_mode_id)) {
-        $form_display->save();
-      }
-    }
-  }
-}
-
 /**
  * Implements hook_ENTITY_TYPE_update() for 'field_storage_config'.
  *
unchanged:
--- a/core/modules/field/field.module
+++ b/core/modules/field/field.module
@@ -335,6 +335,26 @@ function field_form_config_admin_import_form_alter(&$form, FormStateInterface $f
 }
 
 /**
+ * Implements hook_ENTITY_TYPE_insert() for 'field_config'.
+ *
+ * Allow other view modes to update their configuration for the new field.
+ * Otherwise, configuration for view modes won't get updated until the mode
+ * is used for the first time, creating noise in config diffs.
+ *
+ * @see https://www.drupal.org/node/2915036
+ */
+function field_field_config_insert(FieldConfigInterface $field) {
+  if ($field->isSyncing()) {
+    // Don't change anything during a configuration sync.
+    return;
+  }
+
+  /** @var \Drupal\field\EntityDisplayRebuilder $display_rebuilder */
+  $display_rebuilder = \Drupal::service('field.entity_display_rebuilder');
+  $display_rebuilder->rebuildEntityTypeDisplays($field->getTargetEntityTypeId());
+}
+
+/**
  * Implements hook_ENTITY_TYPE_update() for 'field_storage_config'.
  *
  * Reset the field handler settings, when the storage target_type is changed on
only in patch2:
unchanged:
--- a/core/modules/field/field.services.yml
+++ b/core/modules/field/field.services.yml
@@ -5,3 +5,6 @@ services:
       - { name: module_install.uninstall_validator }
     arguments: ['@entity_type.manager', '@string_translation', '@plugin.manager.field.field_type']
     lazy: true
+  field.entity_display_rebuilder:
+    class: Drupal\field\EntityDisplayRebuilder
+    arguments: ['@entity_type.manager', '@entity_display.repository', '@entity_type.bundle.info']
only in patch2:
unchanged:
--- /dev/null
+++ b/core/modules/field/src/EntityDisplayRebuilder.php
@@ -0,0 +1,91 @@
+<?php
+
+namespace Drupal\field;
+
+use Drupal\Core\Entity\EntityDisplayRepositoryInterface;
+use Drupal\Core\Entity\EntityTypeInterface;
+use Drupal\Core\Entity\EntityTypeManagerInterface;
+use Drupal\Core\Entity\Entity\EntityViewDisplay;
+use Drupal\Core\Entity\Entity\EntityFormDisplay;
+
+/**
+ * Rebuilds displays.
+ */
+class EntityDisplayRebuilder {
+
+  /**
+   * The field storage config storage.
+   *
+   * @var \Drupal\Core\Entity\EntityTypeManager
+   */
+  protected $entityTypeManager;
+
+  /**
+   * The display repository.
+   *
+   * @var \Drupal\Core\Entity\EntityDisplayRepository
+   */
+  protected $entityDisplayRepository;
+
+  /**
+   * Constructs a new EntityDisplayRebuilder.
+   *
+   * @param \Drupal\Core\Entity\EntityTypeManagerInterface $entity_type_manager
+   *   The entity manager.
+   * @param \Drupal\Core\Entity\EntityDisplayRepositoryInterface $entity_display_repository
+   *   The entity display repository.
+   */
+  public function __construct(EntityTypeManagerInterface $entity_type_manager, EntityDisplayRepositoryInterface $entity_display_repository) {
+    $this->entityTypeManager = $entity_type_manager;
+    $this->entityDisplayRepository = $entity_display_repository;
+  }
+
+  /**
+   * Rebuild displays for all Entity Types.
+   */
+  public function rebuildAllEntityTypeDisplays() {
+
+    // Loop through all entity types.
+    $entity_types = $this->entityTypeManager->getDefinitions();
+    foreach ($entity_types as $entity_type_id => $entity_type_definition) {
+      $this->rebuildEntityTypeDisplays($entity_type_id);
+    }
+
+  }
+
+  /**
+   * Rebuild displays for single Entity Type.
+   *
+   * @param string $entity_type_id
+   *    The entity type machine name.
+   */
+  public function rebuildEntityTypeDisplays($entity_type_id) {
+    // Loop through all bundles.
+    $entity_bundles = entity_get_bundles($entity_type_id); // @todo: inject service here.
+    foreach ($entity_bundles as $bundle => $bundle_definition) {
+
+      // Get the displays.
+      $view_modes = $this->entityDisplayRepository->getViewModes($entity_type_id);
+      $form_modes = $this->entityDisplayRepository->getFormModes($entity_type_id);
+      // Explicitly add the default displays.
+      $view_modes['default'] = ['status' => TRUE];
+      $form_modes['default'] = ['status' => TRUE];
+
+      // Update view modes displays.
+      foreach ($view_modes as $view_mode_id => $view_mode) {
+        if ($display = EntityViewDisplay::load($entity_type_id . '.' . $bundle . '.' . $view_mode_id)) {
+          $display->save();
+        }
+      }
+      // Update form modes displays.
+      foreach ($form_modes as $form_mode_id => $form_mode) {
+        if ($form_display = EntityFormDisplay::load($entity_type_id . '.' . $bundle . '.' . $form_mode_id)) {
+          $form_display->save();
+        }
+      }
+
+    }
+
+  }
+
+}