I just asked
Disneyland that same question via chat on their website. I was told early August but the date could change. Not the answer I was looking for, but maybe they really don't know the specific date. Also, the DL website says this right now if you try to book a package:
Scheduled Maintenance Planned
While we work to provide the best possible Guest experience, Resort reservation services will be unavailable from 3:00 PM Pacific Time on July 13, 2016 until the morning on July 14, 2016—both online and at our Resort contact center.
Please be aware that this interruption of service will also likely affect your ability to review existing Resort reservations or make a payment for an upcoming visit. We apologize for any inconvenience this may cause.
In the meantime, other Resort services—including the ability to
purchase theme park tickets and
book dining reservations—are expected to be operational as normal.
Maybe 2017 package dates will be available shortly after that....