The earliest this park should have opened is October, with Wet 'N Wild running a shortened season through the weekend after Labor Day, and then transitioning into some soft openings immediately after that. Given that Universal won't even have approval for the new hotels until next week at the earliest, it couldn't have really put them that far behind on the new hotels. The Volcano Bay expansion plot probably could have been built out this summer as well.
An October opening still catches the Fall Break/Columbus Day/Canadian Thanksgiving crowds, and then any kinks can be worked out prior to Thanksgiving.