I agree that right now, most people shouldn't give this a try. But at some point it will reach a steady state.

Either Beeper manages to make a client that is truly indistinguishable from old iPhones, and gets to exist for a few years, or Apple somehow manages to patch all existing iPhones in a way that makes it impossible to spoof (not sure if that's possible with old hardware that don't have a secure enclave).