I see a bunch of Arduino as a programmer hacks. When you upload this way, are you essentially just doing serial? I am confused on how it is different from the AVR ISP. Does the AVR ISP program via SPI? Would it be possible to have a multiplexer control the lines between two other chips so I can program each via serial? Or does that sound just plain ugly? I am guessing an addressable protocol would be a more elegant solution, but it would require more tweaking of the arduino boot loader and code?
the method is using an arduino as an ISP, they are for the most part the same
as far as multiplexing, I doubt that as avrdude doesnt support it, but maybe with some software you could have it upload a chip, switch over and re-run the command as if you were manually doing it yourself