Yay for http://dev.ckeditor.com/ticket/10191 :)

gistfile1.diff

 core/modules/ckeditor/js/ckeditor.admin.js |   35 ++++++++--------------------
 1 file changed, 10 insertions(+), 25 deletions(-)

diff --git a/core/modules/ckeditor/js/ckeditor.admin.js b/core/modules/ckeditor/js/ckeditor.admin.js
index a483296..7d0d755 100644
--- a/core/modules/ckeditor/js/ckeditor.admin.js
+++ b/core/modules/ckeditor/js/ckeditor.admin.js
@@ -206,43 +206,28 @@ Drupal.behaviors.ckeditorAdmin = {
      * Asynchronously retrieve the metadata for all available CKEditor features.
      */
     function getCKEditorFeatures(CKEditorConfig, callback) {
-      // @todo D8 get rid of this once CKEditor introduces requiredStyles,
-      // requiredAttributes and requiredClasses.
-      // See http://dev.ckeditor.com/ticket/10191.
-      var parseCKEPropertiesList = function(CKEPropertiesList, required, allowed) {
-        if (typeof CKEPropertiesList !== 'string') {
-          return;
-        }
-
-        var properties = CKEPropertiesList.split(',');
-        for (var i = 0; i < properties.length; i++) {
-          var property = properties[i];
-          if (property[0] === '!') {
-            var actual = property.substring(1);
-            allowed.push(actual);
-            required.push(actual);
-          }
-          else {
-            allowed.push(property);
-          }
-        }
+      var getProperties = function(CKEPropertiesList) {
+        return (_.isObject(CKEPropertiesList)) ? _.keys(CKEPropertiesList) : [];
       };
-
       var convertCKERulesToEditorFeature = function (feature, CKEFeatureRules) {
         for (var i = 0; i < CKEFeatureRules.length; i++) {
           var CKERule = CKEFeatureRules[i];
           var rule = new Drupal.EditorFeatureHTMLRule();
 
           // Tags.
-          var tags = CKERule.elements.split(/\W+/);
+          var tags = getProperties(CKERule.elements);
           rule.required.tags = (CKERule.propertiesOnly) ? [] : tags;
           rule.allowed.tags = tags;
           // Attributes.
-          parseCKEPropertiesList(CKERule.attributes, rule.required.attributes, rule.allowed.attributes);
+          rule.required.attributes = getProperties(CKERule.requiredAttributes);
+          rule.allowed.attributes = getProperties(CKERule.attributes);
           // Styles.
-          parseCKEPropertiesList(CKERule.styles, rule.required.styles, rule.allowed.styles);
+          rule.required.styles = getProperties(CKERule.requiredStyles);
+          rule.allowed.styles = getProperties(CKERule.styles);
           // Classes.
-          parseCKEPropertiesList(CKERule.classes, rule.required.classes, rule.allowed.classes);
+          rule.required.classes = getProperties(CKERule.requiredClasses);
+          rule.allowed.classes = getProperties(CKERule.classes);
+
           // Raw.
           rule.raw = CKERule;