Hey,
i think it is an cool idea - for an cool editor look at http://ace.ajax.org/
and for the upload thing:
it would be easy for the user to just download a small app for the browser he is using.
so if it would be possible to pack the avr upload things in the app - great thing..
for me as an sometimes proffessional user - i don't want to upload the code somewhere -
so it would be great to have an 'easy to install' server for the own editor system - or the complete compiler system in the app -
this would be cool - i often work together with colleges and if every body could look and use the latest versions ... dream on
sunny greetings
stefan