I just found this thread - two years after it began.
As an Optus customer, with multiple devices on the Optus network - I'd been Googling for information about whether there has been any progress with Optus implementing the RCS chat feature.
Alas, I'm saddened to see there is no progress after two years.
This adds to my other Optus network gripe - that inter-network connectivity fails on certain phone numbers because Optus does not update its number porting database list. Come on Optus, you are failing in multiple areas. Please get your act together.