What you're describing is WhatsApp. So we don't need to speculate.

iMessage benefited tremendously from being the default. Combine that with Apple's mobile market share in the US and you get the present situation.

My gripe isn't really that it won in the US. Its that you need Apple hardware to participate.

Google may be self interested but they're right about one thing: knowingly allowing and fueling this social dynamic is inconsistent with Apple's brand. But it was never really about values, just making consumers feel good about their purchases.