this would only work for a vary narrow range of setups.
many people don't keep the files locallaly and STILL don't want to download them.
any sort of epispde tracking will need SOME sort of database (not saying it will need an sql type db) to keep track of which files it has downloaded, and it will also need logic to figure out what is consider a match.
PErsonally, i do not believe this is needed. You can get results which work fine using the system we currently have. If someone else wants to write a plugin, or submit patches against ours, we'd be happy to see either.