> As to messaging apps, SMS and email work just fine but for anyone who cares I suspect they would simply jump to whatever messaging app did work.
Absolutely not. Telecommunications applications have extremely strong network effects. There is no jumping ship to whatever works, people will do whatever is necessary to join the network their social circles participate in. In my country it's virtually impossible to communicate without WhatsApp. People buy phones just to run WhatsApp. I've had Signal installed for years and I've not received a single message there, not even from technologically minded friends who really should know better.
Absolutely not. Telecommunications applications have extremely strong network effects. There is no jumping ship to whatever works, people will do whatever is necessary to join the network their social circles participate in. In my country it's virtually impossible to communicate without WhatsApp. People buy phones just to run WhatsApp. I've had Signal installed for years and I've not received a single message there, not even from technologically minded friends who really should know better.