FEATURE: Hidden site setting to always include topic excerpt

app/serializers/listable_topic_serializer.rb

@@ -108,7 +108,7 @@ class ListableTopicSerializer < BasicTopicSerializer
   alias :include_new_posts? :has_user_data
 
   def include_excerpt?
-    pinned
+    pinned || SiteSetting.always_include_topic_excerpts
   end
 
   def pinned

config/site_settings.yml

@@ -1768,6 +1768,10 @@ uncategorized:
     list_type: "compact"
     client: true
 
+  always_include_topic_excerpts:
+    default: false
+    hidden: true
+
 user_preferences:
   default_email_digest_frequency:
     enum: "DigestEmailSiteSetting"