I got a call from concierge this afternoon and got the same information you did. According to the concierge manager
DCL is going to enforce the port arrival times and there will be a separate queue area for those people who did not check-in online and select a port arrival time. She also told me that boarding time will not change. I think someone posted this before but this makes me think of bus stops at WDW. I can see different lines for each arrival time and if you show up prior to your arrival time then you will have to wait in your appointed queue area.
With the port arrival times it sounds like they are trying to alleviate some of the crowding in the terminal. And with the terminal not opening until 11am, it sounds like they are trying to alleviate some of the congestion outside the terminal with some cruisers leaving and new cruisers trying to show up.
I guess we will see what happens on August 2nd.