Now instead of "USE SMS" it can (and should) negotiate an RCS connection.
Except that it shouldn’t… unless the assumption is that every phone is a smartphone, which it isn’t. I can understand how folks that grew up in a world where smartphones are what most of the people around
them have, may have a slightly altered view of reality which might lead them to such a conclusion.
For someone on AT&T in the US, if the fallback from iMessage is RCS, then that message is excluding the majority of folks that live on the planet. Based on the current market numbers, a person isn’t even able to reach most of the folks in the US! Stepping away from the carrier based SMS solution, even when considering Google’s “just another app” Google RCS, that’s STILL a minority of phones, not even most Google Android phones can use Google RCS. And, once a person has decided that “just another app” solutions are acceptable, do you know what a huge number of those Android phones that can’t use Google RCS CAN use? WhatsApp… which is the cross-platform solution the vast majority of folks use.
What is being proposed through this thread and effort is to use better communication where it is available, not to replace anything in iMessage-land, or fundamentally alter the ecosystem. It's about providing a telco-wide upgrade in messaging security and functionality.
If this was about Samsung, Motorola, Apple and whatever other handset companies communicating to the carriers about supporting a more advanced protocol, then THAT would be about providing a telco-wide upgrade in messaging security and functionality. Because this thread is about Google pushing Google RCS, this thread is about their “just another app” solution, which even most Android phones don’t support, far short of “telco-wide”. WhatsApp has a wider reach and they don’t even have agreements with carriers!
Your response above is solely assuming that if you want the 70% of the world's phones to communicate with Apple devices in the same security they must use 3rd party apps.
Well, that IS what exists in reality right now. And, if it was something arduous or onerous, if it was “terrible” or caused “suffering” as some like to state, it wouldn’t have taken off like it has, removing millions of dollars of SMS fees from the carriers. I don’t even have to speculate on some potential future time… Right now, folks that want to communicate, specifically encrypted, between iPhones and Android devices are doing so quite effectively.
Apple has yet to even come to the table to entertain a RCS answer or discussion.
Because RCS, as it exists, is going nowhere. Everyone knows it, GSMA has abandoned it. The last push in the US for something that used RCS was the CCMI (Cross Carrier Messaging Initiative) that the carriers were working on
without Apple, there’s no need for Apple to be a part of the conversation as they’ll just support whatever the carriers dictate, just like with SMS/MMS. The best thing now would be for the carriers to go back to square one and contract with someone to focus on the interoperability from the start, bring that up at a future GSMA meeting and try again. Whatever poison RCS carries with it that kills every attempt at implementation (that would make it more than “just another app”) needs to be left behind. Unfortunately, Google, desperate to find a path to a ‘win’ in messaging won’t let it die!
Or better yet, Apple needs to say to within all green bubble conversations "This conversation is unencrypted. Please use a 3rd party app for greater security." They can't have it both ways and tout security while not using it or advocating their own risk vectors.
The carriers wouldn’t allow Apple to do anything even remotely resembling that.

And if Apple tried, Apple would quickly find themselves without carrier support, worldwide. The carriers control the hardware connection requirements, with all the insecurity that SMS entails, for their financial benefit. And there’s no handset maker that’s ever going to be allowed to turn off that spigot.