Saw this in action on recent round trip BOS-SFO. Had middle/aisle at back of plane both flights, and boarded in Group C both times for both of us, so they aren't splitting up groups on the same PNR.

I can't accurately say if there was a change in boarding time, as this was my first A321 flight, but both boardings (particularly outbound from BOS) seemed to take forever. Flight back wasn't full, so that helped, but boarding was pretty slow, and gate agents seemed to be allowing long pauses between boarding groups (presumably to let the aisle clear out).

I know I'm overly skeptical, but it still seems like these changes are just shuffling the deck chairs - as long as we're boarding humans it's not going to work well. ;-)