It's a morning of panic for /mlp/. Mainly because those who have tried to get onto it this morning, have been greeted by a grim sight: this page. /mlp/ isn't even there anymore. What is going on?!
There is no need to panic however.
While initially it appeared that /mlp/ was removed from the board, it appears that whatever is going on is affecting every "blue" board on 4chan. The boards are completely empty, and in most cases are missing their titles. The "Red" boards have also been affected, but in a different way, as all posting has ceased. The above screencap from /b/ (the fastest board) indicates that the event that knocked the site offline occurred at 5:12 am EST this morning.
There's no indication from any official source as the cause of this apparent failure, however, 4chan traditionally performs its server and site maintenance activities on Sundays. This very well could be the first maintenance after Moot's departure, and somebody just forgot to put out the warning.
Dedicated /mlp/ users have departed for MLPchan as is their standard contingency plan for /mlp/'s disappearance. The "/mlp/" is down thread is located here.