Yes, it is a global standard and has been for a number of years as previously stated in this thread.
What Google has done is put together a version that is compatible across the RCS landscape.
Except that it’s not. If Apple were to implement standard RCS in iMessages, there still wouldn’t be end to end encryption, for instance, as that’s only available as part of the special sauce Google puts on top of RCS when you use Google Messages, it’s not baked into the RCS protocol. Most of iMessage’s functionality (or of Facebook Messenger’s equivalent functionality) wouldn’t be available, either. Google has completely oversold what RCS is, it’s basically an extension to MMS with longer messages and better support for group chat. And Apple already attempts to abstract away those aspects of SMS/MMS, you can send long messages but they’re split into multiple SMS packets on the backend and displayed as one message on the frontend, and you can kinda do group SMS, it just sometimes is fragile. Well, it also allows for read receipts and typing indicators, as well.
Standardized RCS doesn’t actually support most of the modern chat effects iMessage, Facebook, etc. have had for years. In-line replies, text backgrounds, reactions, RCS has no ability to do any of that. So RCS basically is green chat bubbles with read receipts and typing indicator. And that’s because it’s a standard that dates back to 2008.
Google Messenger is
not RCS. Google Messenger is a layer on top of RCS that adds modern chat features. But that only works if both RCS gateways support those features, and those features are proprietary to Google Messenger. You have to go through Google’s RCS gateway to get them, and Google isn’t going to let Apple go through their gateway (and nor would Apple want to). Google doesn’t publish intercompatibility documents for other RCS providers, to the best of my knowledge. So while Apple may be doing messaging lock-in with iMessage, Google is doing lock-in on top of what’s supposedly an open standard (good old embrace, extend, extinguish) but claiming that their proprietary implementation is still the open standard.