Sure, though my use case would look more like treating multiple destination devices as one logical AND, and running the backup only when all are present. I wouldn't need any guarantees w/r/t which files land on which device or the order they're written to, only that if sum(destination device storage) > size of folder to be backed up, everything from the folder makes it onto one of the devices.

OK, I see. That's a good case, let me think about it.