These are not incompatible with private servers. I can imagine a world where, on setting up your phone, you set up the location of the backup server, which can

These are not incompatible with private servers. I can imagine a world where, on setting up your phone, you set up the location of the backup server, which can be a server that you own. On taking a picture, instead of syncing with Google/Apple photos, it syncs with the server that you have chosen. When you share a photo, it indicates that that photo should temporarily be moved from a private folder to a public folder on the backup server.