Didn't know about this new process until Sunday, when one colleague was in 13A (group C) and another was in 13C (group E). They were on separate PNRs with printed boarding passes. I was in 14A on the same PNR as 13C, but I have no idea what boarding group I was in, since it doesn't appear on the mobile boarding pass in the app. So I boarded with 13A. And 13C boarded right after me, since I was able to swipe to his boarding pass on my phone and thus they didn't know which group he was in -- I was surprised they allowed two boarding passes from the same phone!

Seth