We are staying at the GCH opening weekend of ROTR (not on purpose!!), and I have not been informed of any perks (like we had for SWGE opening reservation weeks, which was also attended).
Looks like 3 days in a row at WDW of letting people scan into the park about 30 minutes before park opening, and then opening the ability to book a BG right at park opening time. I seriously hope that they do this at DLR. It allows you to get a BG, then go to another park, go on other rides, go back to the hotel or go back to your house and take a nap, and then return in the 2 hour window when your group is called. Standing in a 9 hour standby line would be horrible since you can't do anything else with that time. And as OP stated, ride breakdowns (sometimes for a few hours) occurred at WDW often in the first week. They gave those in the line and on the ride a paper FP to come back later that day (and in some cases the next day) to ride again, without regard to what BG was active at that time. If they had to do this for all of the people in a 9 hour line, it would be a nightmare. Would make it impossible to plan BGs for the next day since you would have so many with "anytime" FPs to ride ROTR from the prior day's breakdown.
The downside to BGs is that once they are out for the day (usually in the first hour or less of park opening), you can't ride (they have now started back up BGs that may or may not get called, but they get no compensation if they don't get to ride due to breakdowns etc; those are filled within about 2 hours of park opening currently). Since there is no SB, you have to get to the park early or you miss out. Maybe sometime later, they will start issuing BGs later in the day if they get through all the regular BGs and all of the backup BGs, but who knows. So for later arriving guests, BGs do have a disadvantage. To me, it is still a much better solution than simply SB.