I'd love to see a library for Android's key/value backup service:
https://developer.android.com/guide/topics/data/keyvaluebackup
This service lets any Android app (since Android 2.2) back up their settings data, so that if the app is reinstalled later (on the original device or a new one, like when you get a new phone), the user's configuration data is restored.
Android currently provides an Auto Backup service which works fine, but only if the old and new device are both Android 6+. I'm still supporting Android 4.x and 5.x users, so I'm keen to add automatic backup/restore for when they move to a new phone.
My Java is barely rudimentary (been spoiled by B4A for a long time now), otherwise I'd give this a go myself.
Cheers!