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…
Sadly the code quality is prototypical at best and while I still use the app multiple times per week, I never released it and have quite a few leanings which I want to implement (like rewriting the sync logic in a separate library, changing the server side data model to improve performance, completely reorganize the user interface and add more features to the app), but aren't coming to due to other priorities.
However, what I also learnt is that it is possible to build something like it, even if your use-case includes advanced topics like offline collaboration. My hope is that one day we will have a library that make these things for developers as easy as firebase and every app will have it out of the box.