Neither Apple nor Microsoft allow you to plug-in your own sync adapter. What if you do not want to use CalDAV/CardDAV, but your own protocol? For example, Sams

Neither Apple nor Microsoft allow you to plug-in your own sync adapter. What if you do not want to use CalDAV/CardDAV, but your own protocol? For example, Samsung, Asus and Sony do exactly that. They provide their own sync adapters. Maybe that's more important to them (and their customers) than generic CalDAV/CardDAV.