It seems that the reason for the delay was due to Ubisoft choosing to focus on the 1.06 update to the game. “Watch Dogs 2’s 1.06 title update has just been released across all platforms. This and previous patches were an important step towards stabilizing Watch Dogs 2’s seamless multiplayer functionality, and other core online features, before releasing any new multiplayer content. Since these updates required additional development resources, we’ve made the decision to adjust our release schedule for that new content.”
We suppose better late than never, and also better late than Ubisoft rushing out DLC that has subpar quality just so that they can meet a deadline. We’ve seen multiple instances in which rushed games have resulted in quite a bit of backlash, so it’s not necessarily a bad thing that the DLC’s release has been delayed.