To be able to sync/backup things like WhatsApp Media it needs to be possible to grant an application access to ~/.android_storage/Android/media/com.whatsapp, I can imagine the same/similar would apply to other android apps a user may want to sync.
While I understand that granting access to the storage of a different application is not always ideal I am wondering how this could be done in an ideal world.
(I rsync ~ periodically, but I use sailsync owncloud from constant syncing of pictures/videos to my nextcloud).