A theory I've cooked up about Sunday's debacle by observing this thread:
It seems clear after today that the general policy for opening Hollywood Studios on non-EMH days is 6:30 AM or when the line at the tapstyles reaches the security checkpoint, whichever happens first.
(As a quick editorial, I think this is a bad move. Disney should be trying to push the opening closer to its posted time, not further. The longer they keep letting the crowds open the park at 6:30, the more people will learn about the practice, and the harder it will be to open on time. They really ought to do it the other way around: whichever of those two scenarios occurs last.)
I think the plan for EMH day was to give EMH guests a 15 minute head start on Boarding Passes (thus the 7:45 opening they initially announced) and then to release everyone in the normal entry queue into the park. But at some point, they moved up the regular park openings to 8 AM for the next week, so they had to bump EMH even earlier to accommodate the on-site guests. The real break in communication though happened on Sunday morning. The regular guests were stacking up in the entrance to the point where they were going to reach the security checkpoint well before the 8 AM open time, which - as mentioned above - would prompt them to open the gates. So now the park was going to open earlier than 8, which means the Virtual Queue would have to open earlier than 7:45. Only the decision to do the former did not reach the people in charge of maintaining the latter in time to give EMH guests their 15 minute window. It was, at best, a 5 minute one that only benefitted the guests feverishly checking their phones. To make matters worse, as the regular guests stacked up on the entrance the park staff carried out the standard procedure of admitting them through the tapstyles and into the front section of the park proper - meaning the first few hundred or so people in the regular line were now eligible for the same Virtual Queue headstart as the EMH guests.
As for what happened after the VQ opened, I'm not sure. BGs went in a quarter of their usual time, which would suggest that 4 times as many people were in the park as on prior days (which I suppose could have been possible if only because Disney actually advertised the hours they were letting people in). But basically, the off-site crowd waiting to enter the park at 8 was so large that it preempted any attempt to give on-site guests an advantage. The only reason I can think of for why Disney didn't expand the VQ to open at 6 AM is that they thought EMH guests would take all the Boarding Groups before the regular guests arrived, which I don't think holds water. It seems like BG1-10 are reserved for EMH guests in the first place. But it still begs the question: Why did they open at 6 at all if the party was never going to start until after 7?