[Jtsummers]

If messaging clients like WhatsApp permitted a Keybase styled authentication of additional devices, then migration (so long as the original were available) wouldn't be difficult at all. And if they permitted backup to a user selected service (for instance, Google's for Android versus Apple's for iOS) then migration across OSes would become simplified for users.

But the WhatsApp iOS client backs up to iCloud, and the Android client backs up to Google, and this creates a blocking issue unless the user is willing to jump through hoops and use 3rd party tools.

[snvzz]

Matrix actually does authenticate additional devices, and handle all that.

It's already out there, just a matter of adopting it.