Apple's Time Capsule can act as both a backup drive and a network shared drive at the same time. Can it backup its own data to incremental backups? I can't find this information anywhere. I've not used Time Machine so I don't know if it can be configured to backup shared drives (independently of whether Time Capsule has the option).
I would like this to be a feasible way of freeing up some storage on an older MacBook Air by keeping large media such as photos archived on the drive like you would a USB external drive. But having the only copy accessible throughout the house and not backed up would make me nervous. I like the idea of having a good router, network storage and backup in one box, although obviously it's safer to backup the Capsule itself to USB occasionally too. Other solutions to this are of course welcome if this is not possible.