That text seems more a reflection of the fact that only Messages supported it, when the document was written
If they seriously wanted random third parties to implement it, anyhow, they'd have published a specification, not an "overview"
If they seriously wanted random third parties to implement it, anyhow, they'd have published a specification, not an "overview"
At this point I think they just wanted to get rid of their SMS backup feature and used RCS as an excuse.
Put another way, if this was a Signal thing what other Android app is doing this?
("Only Messages was allowed to support it. At the time it was written, for example, it was years after the Signal developers had asked for basic RCS support (2015) and given up on Google relenting and allowing it in 2018")