It would be a non-issue if Apple would let me pick a different SMS client. I could pick one that uses RCS or any other protocol I wish like WhatsApp, but as usual Apple knows best.
You can use WhatsApp or any other third party app that you choose as long as it’s on the App Store.
Apple will not, and should not, integrate any third party app/protocol into iMessage - who guarantees the security of the messages, Facebook? Google? Yeah right.
Carrier protocols like SMS or RCS yes, but face it, RCS is a hot mess of different technology with uneven support in the US and little support outside the US. I don’t blame them for not embracing RCS.
From another site:
’Not all carriers and devices support the protocol and it can be implemented in different ways, such as encryption.
Like SMS, RCS relies on an active phone number. Texting gets tied to a cellular bill and can vanish if a payment is missed or because of other cellular network chicanery.’