Yes, it's already largely done, but that doesn't mean it was a good idea, so why cheer moving into the same bad direction just because there's now finally a baseline of security?
It's also anything but indistinguishable from iMessage. I can use iMessage on any number of devices without my phone having to be turned on, having the SIM with my number on it inserted, and being connected to the Internet (not always a given when traveling etc.)
The same is true for WhatsApp. Even XMPP could do it 20 years ago! This is not a new niche feature – it's absolutely essential for a modern instant messaging protocol!
No, I'd rather we have an actually open, federated standard such as XMPP or Matrix, with a trusted directory service binding phone numbers (that one could be operated by phone networks) and email addresses or DNS domains to IM handles.
And if we can't figure that out, I consider Google and Meta equally bad gatekeepers of global B2C and P2P communication, and don't see why I should use the technically strictly inferior solution of the two.
It's also anything but indistinguishable from iMessage. I can use iMessage on any number of devices without my phone having to be turned on, having the SIM with my number on it inserted, and being connected to the Internet (not always a given when traveling etc.)
The same is true for WhatsApp. Even XMPP could do it 20 years ago! This is not a new niche feature – it's absolutely essential for a modern instant messaging protocol!