A real-time feed of external links is overkill. As mentioned by others, the chief problem is linkrot of old links. All we need to do is dump the contents of externallinks.el_to from the database once a year or so, run a hex to ASCII conversion on it, zip it, and email it to someone at the Internet Archive. Anyone with access to the databases should be able to do this fairly easily. Rather than trying to engineer a complicated system that will take a year to implement, why not take this simple approach that will take care of 90+% of the problem?
Ryan Kaldari