Today Vyvyanne announced on the forums that Update 18 has been pushed back a day to fix an unspecified bug. The update is now set to release on Tuesday April 12th.
“We do not formally announce launch dates (in writing here or on the launcher) until all is through the final QA checks and we are confirmed for live which is anywhere from 3 days to 24 hours depending on the build type. We did run into a last minute high severity bug that prevented us from hitting April 11th, we are now targeting Tuesday. Since we have the extra day, I chose too put out the final build on Beta for the weekend just in case Beta players find any big issues that would make me push the big red stop button for going out on Tuesday.” – source
The update has also been officially titled The Battle of Pelennor Fields.
More info on Update 18: