https://rclone.org https://rclone.org is a very effective storage shim. You'd still want to limit supported backends to provide a smooth UX. There are binaries

https://rclone.org https://rclone.org is a very effective storage shim. You'd still want to limit supported backends to provide a smooth UX. There are binaries for the major OSs (including BSDs, Plan9, and Solaris). They have Android builds but they are not first class (yet). Unfortunately I do not see any support for iOS.