You say no human intervention....so who's deciding when to load the new firmware?
I meant there wouldn't be anyone physically at the device. The device has internet connectivity so the HEX files can be transferred that way.

There are, for example, bootloaders available which reads the code from a memory card (CF, SD, MMC etc). I don't know of any written in PBP though.
This would be a good kickstarter project. Any takers?