I saw the 'rapid transfer' tags in BCN and AMS in Sept. If I recall I think I saw some in AUA as well.
At the time I just assumed it was for international locations to assist with transfers for places that may not have as good of a baggage system as most of the US, but guess its appearing domestic as well. I'm all for anything that could help flag bags that have tighter connections to make sure they get there on time.

As for the priority tags and 20 min - yeah that doesn't seem to have any impact in BOS, as its a sure thing when I check a bag that I'll get the miles for the bags on time claim.