If I am understanding the test correctly, they are not simply dumping all available slots into the MDE system for preselection. As I understand it, the number of FP+s available for prereservation isn't changing. Instead, they are holding back all of the one's previously alloted to SB. They are then, as some one put it, priming the pump with an hours worth of guests in line and then allowing FP+ assignment for the remainder of the slots.What I mean by that is Anna and Elsa FPs 99% of the time are gone on the 60 day mark and most people can't even get a FP for it on their 60th booking day. How are they telling guests to get a FP+ for it when all the fast passes are gone?!? Sure they can hand out more fast passes, but all that is gonna do is still keep the line very long and not reduce the line like they are claiming with this new set up. This doesn't solve the line problem at all.
The downside of this test is the same as for every previous test. Those that show up in the afternoon are unable to wait in a long line to see S&E. It doesn't freeze out 'day of' guests from being able to do the M&G, however.