If I had to guess, I would assume they will handle it exactly like the did the initial opening of GE. They will start the Boarding Groups again and you will not be able to enter GE unless you have a reservation or are part of that current Boarding Group. If anyone remembers how far back the lines were for FoP when it opened, which were back all the way across the bridge, I can safely assume they don't want that happening in GE. There's so much riding on the opening of this ride that I would submit they are going to do everything they can to make sure it's as pleasurable as possible with minimal frustration for all involved.
The Boarding Groups worked well and I would think that's why you have not seen it leave the
MDE app, because they always planned to utilize it for the RotR opening as well.
I am there the first week of December. I have chosen to skip opening day and go the next day. That may what everyone else does as well and it may turn out to be even worse, but we will just have to see.