When either Phabricator or Gerrit are down for maintenance, users are greeted with a generic 503 error page. This is less than ideal because it's difficult to tell the difference between scheduled maintenance and an unplanned outage. It would be nice if we had a way to trigger an alternate error page to be displayed by the front-end proxies when the service is in a scheduled downtime instead of an outage.
For bonus points: Phabricator could provide an in-page notification a few minutes ahead of time to give users a heads' up before the service goes offline. This, I believe, could be easily accomplished by using the newly-implemented phabricator real-time notification server.