Ive been testing RCS on this release. I was finally able to get it activated using an earlier build (and then updating to the latest one using Google Play), however, not much more than that.
I am unable to initiate RCS chats, nor am I able to receive RCS messages. When someone tries to message me, I don't receive the message unless they fallback to SMS/MMS. I tested with a spare Google Android phone with RCS confirmed working.
I am on Tello (which uses the T-Mobile network)
Update: A device reboot fixed it. RCS works!! God bless, you're angels.