As someone dabbling with such an app right now, there are several hurdles if you want to exclusively use self sovereign identity. 1. Local data gets lost, so you need to sync for backup. But when your device gets lost or when you need to access it from elsewhere, how would you login to the said backup service? The most intuitive option is still a username and a password. 2. It's hard to transfer data from one device…
a) what's a thumbdrive?
and
b) what's local data?
Each answer resulted in even more questions. Why isn't it in the cloud? What do you mean I'd have to copy it again? I can run out of room?
I could understand needing to get across to some people that not all data ends up synced (eg, saved memes are not necessarily automatically backed up to Drive)... but reaching a point to where people could be completely unaware of USB storage media actually shook me to my core.
People now expect it all to just "be there" after they log in.