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. ;-)

No matter what boarding process they use, it will always take longer than any simulation they perform in Long Island City. There will always be those customers who take there sweet time blocking the aisle because they don't know where row 12 seat C is. I've been on multiple airlines recently and there is no easy solution. Very frustrating to those of us who board and find our seats and are ready to go.

I believe EMS is Group A. GA was very specific that Military/Families board after Mosaics. Perhaps someone else who is non-Mosaic but EMS can confirm this.

This weekend at SFO (and I believe earlier at BOS), Group A was EMS and uniformed military, as it was announced in SFO.

As an aside, the monitors at SFO (the airport's common use system in Terminal A) helpfully indicated which group was boarding (including labeling the first group Mint and Mosaic, so it was customized for B6), but no such feature at BOS. :-/

I was on BOS -> ORD round trip yesterday morning/night, maybe it was just a predominantly business crowd, but it seemed really quick and easy boarding each way.

Boarding Process
 

I've always believed, the best way for airlines to do the boarding process is to board those WITHOUT CARRY ON'S FIRST. That way those that do not have carry on's can take their seats while the rest of the flyers flight for overhead space.

Can you elaborate on why you think the only people who have no need for overhead space would want to board early?

That makes no sense. The whole point of boarding early (and airlines monetizing on this by selling priority boarding) is for people to have early access to overhead bins. If they boarded people without carry ons first, you'll end up with bins full of personal items, and a bunch of irate people who will then need to gate check their bags. Not to mention that airlines would no longer be able to sell priority boarding as it would lose its value.

First (or maybe even second) checked bag free. $100 for a carry on. Like seriously penalize carry ons...

You could board a fully loaded A380 in 10 minutes. Single biggest issue I see with boarding speed is infrequent flyers stuffing huge carry on bags into overhead bins. Mosaics and people with an understanding of overhead bag sizes get priority boarding.

I believe Spirit charges more for overhead use than checked.

Board any mainline aircraft with 20%+ of the passengers who are "elite" and you'll see it is still a mess. There's no particular demographic of people who struggle storing bags in overheads.

I travel about twice a year with checked luggage and nothing for the overhead. I would never want to sit on the plane longer when I didn't need to and I'm in the isle with people slamming into my broad shoulders.
No thanks, nothing for the overhead I am last on, ok last without losing my seat.

I spoke with an FA manager from HQ and she told me that for people on the same PNR, you must board with the later group if you want to board together. This has been confirmed by several GA and in practice, from what I've seen.

Hmm, perhaps that's a refinement after launch? Flew earlier this month with two travelers on E190 flights, with 20A/B both flights. Boarded with Group B both times, which should be the first general boarding group (i.e., window seats, back half of plane) IIRC?

Depends if both passengers checked in at the same time