Snazzy Labs has RCS working on his iPhone running Developer Beta 2. See my comments in the Quote Tweet above!
It’s important to note that this feature is only working in the US on Verizon, AT&T, and T-Mobile right now. All three carriers use Google Jibe to facilitate this new communication method, similar to Google Messages. However, because Apple Messages uses the Universal Profile, RCS on iOS does not support end-to-end encryption.