Arthur, you're not making any sense. This isn't rocket surgery.
The iPad can maintain a list of (flash) storage sectors which have changed. When your iPad is in the presence of some sort of NAS device (or cloud storage), it starts backing up the list of sectors that have changed.
If the iOS file system isn't sufficiently sophisticated enough, it can track the changes at the file level. This is what MS DOS 3.3 did with the archive flag on files. When the file is changed, the archive flag is raised, and when the backup software backs up said file, the flag is lowered.
Then, when your iOS device is on your home WiFi network (if your backup is on a NAS device), or when it's connected to the internet (if your backup is configured to use the cloud) it starts backing up the stuff that has changed and hasn't been backed up yet. If you're concerned about battery life, then there could easily be a option to only do backups when it's plugged in and charging.
When it loses WiFi connection, it stops backing up, but remembers how far along it made it. It doesn't need to disrupt the user, it doesn't even need to tell the user "hang on, I'm backing up here...". In fact, it doesn't need to be doing these things while the user is actually using the device.
The reason why I'm amazed by your position is that this is something that computers have been doing for decades now. It's the same pattern. Mac OS X does it, and there is no technical reason why iOS couldn't do it too.
You mention the 64GB of data as if that is some barrier, but Mac OS X devices typically have much more storage, and typically perform operations that would cause more file updates, not less. Yet this doesn't seem to prevent people from successfully using Time Machine.