This is quite different, because Google Talk was a pure data thing, while RCS is something the carriers are going to be keen on. They're particularly keen to be

This is quite different, because Google Talk was a pure data thing, while RCS is something the carriers are going to be keen on. They're particularly keen to be able to sell RCS messaging access to businesses, lest those businesses who are currently buying SMS for things like notifying you when your parcel delivery is due or reminding you of your eye test appointment skip straight over the carriers and start sending people WhatsApp or Facebook messages instead. It could all fall over, and Apple don't seem to be giving any hints about if they'll be supporting it, but so far things are looking pretty promising for this technology. Disclaimer: I work for a company which is a Google partner developing business RCS services for exactly this kind of use case.