It sounds like the difference is that currently, the waiting adult and child(ren) can wait a ways away from the ride queue entrance. Plenty of times, we’ve waved to the waiting members of our party from across a walkway, etc. We’ve even shown CMs a picture of our whole party (from that day, showing us in the same clothes) in instances when the babies were sleeping somewhere and it wasn’t easy to bring them over to the ride.
If the rumored RS changes occur, everyone in the party will have to actually go up to the queue entrance (where the CMs stand at their computers) and have their MBs scanned.
Aside from the pain of the waiting adult having to get the too-short kid(s) from the ride queue entrance to somewhere they can wait after MBs are scanned (not easy to do alone with more than one kid), I think the new policy will definitely clog up the queue entrances. There usually seems to be a mass of people at 7DMT, BTMRR, etc, as it is. I can only imagine it’ll be a disaster when they add in a bunch of extra strollers (and small kids trying to walk, etc) right at the entrances.