Currently on DB2 and no issues to report. iMessage seems snappier and less jittery.

Can report that RCS is working on AT&T. That being said, I received my first RCS message while not being connected to the AT&T network and without WiFi calling being enabled on my phone. Was at home with my phone on WiFi only and received a message from a friend who has an Android phone. I replied with a heart, text and some pictures. The second message failed (its beta) so I turned on the cellular service to complete the conversation.

Just sharing my experience.