This patch was the Pinnacles of Power update. Community Manager, Eric Musco, post the following, in which he cites a last minute issue causing the delay of the 6.1 patch:
“A bit of bad news, we are going to be delaying 6.1. We discovered a last minute issue with the patch today that we need to address before releasing it. I don't currently have the new release timing (as we are actively investigating the issue) but I will let you know as soon as I do. This also means that tomorrow's maintenance is postponed and will coincide with 6.1's new date.”
Patch notes were posted as well, outlining a massive host of tweaks and changes to classes, combat, flashpoints, operations, uprisings, items, economy, and more. You can read them in full here.