Flash with sd card

I'm new to AVRs, but I love them so far... I was thinking about writing a bootloader that would look look for a binary image on an SD/MMC card on boot. If it was there, then flash the AVR from it. It seems this would be handy for in-field upgrades, it would also be extremely fast.....etc, etc. My question is: Has anyone already done an open-source implementation of this idea for the ATMega 2560

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See this:

And tghe source code here:

Also Nick Gammon's implementation: