I honestly believe the friction of paying any non-zero amount at all for a messenger app is more than what 80%+ of users would be willing to bear psychologicall

I honestly believe the friction of paying any non-zero amount at all for a messenger app is more than what 80%+ of users would be willing to bear psychologically. They would almost certainly just migrate to a different app. That's also where WhatsApp's group emphasis becomes a huge drawback - groups would tend to migrate together, making it easier and quicker for the whole network to unravel.