I started a few days ago to build an update tool. Inspired by the rpi-update tool from hexxeh.
It uses the standard scripts from /opt/scripts/
You can check this out at https://github.com/incyi/bbb-update
Still improving, any comments are welcome. 
The call to: "./update_bootloader.sh" is actually a little risky.. I
don't always test for compatibility.
and "./update_initrd.sh" isn't needed as the initrd should be
generated in "./update_kernel.sh"
Regards,