I was wondering if the TFTP (Trivial File Transfer Protocol) could be built into the Ethernet Arduino's bootloader so that during the loading if a pin was held high or low it would enter TFTP Programming mode which would in essence allow you to program the Arduino via Ethernet, i.e. via the TFTP protocol, something which many Routers and similar network based devices offer.
I am unsure on if it would A. be possible or B. be something people would be interested in, but primarily, C. I have no idea how it would be implemented.