I don't think it was planned. There was some countdown for Golden Castle mobs and then it went offline.
The lack of announcement both in game and on the forums is a bit disconcerting. Here's hoping the terrible experience rates were a bug.
Before we jump to conclusions, let us assume the best and work our way toward finding out what occurred. I agree with Blitz, I don't think this was intentional. We'd have an update message about it.