It's not possible because they use different frameworks on each operating system. On iOS, they use Apple's Core Data, which is optimal for what they need, but i

It's not possible because they use different frameworks on each operating system. On iOS, they use Apple's Core Data, which is optimal for what they need, but is not portable as Core Data is closed source. That's not to say that there cannot be a method to do this, just saying the first major hurdle they'd hit.