I'm pretty sure you can save your session file as XML?
Yeah. You could probably create something that works on a single file... But if you separate the XML file by track, etc., into separate files you could use the regular 'diff' tools on it and it would be easy to apply true revision control. You could have people editing different tracks of a single session over a network and those changes could be added into the main project through patches. And later you could go back and undo changes on individual pieces... Kind of like a perpetual undo feature...
I have done some pretty basic work in this area - <http://www.mediasweeper.com.au>
but more effort and knowledge could lead to more trinkets and baubles
Actually I knew you had something to do with media sweeper... I've used it before and it does the job... Thanks for that tool btw

Any source code?
I'd suggest a collaberative project, but to be honest I've been pretty busy with this stupid data entry stuff and I'm not that familiar with windows gui programming... I'm good at working with the unknown and using hex editors in my spare time though...
Oh yeah... Here is a question maybe only Adobe can answer... I don't have AA3 here on this computer so I can't be sure, but if AA3 uses an SSF plug-in for the .ses files... Would it be possible or even legal to use that plug-in in third-party software (used from AA installation and not redistributed of course)? or is it internal like I suspect?