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What might it cost to buy off the data to a reliable datastore? Could the format of the data be opened to let outsiders write the processing tools?

No idea and probably not. The Bloglines podserver/itemdb was built internally. You can get some idea of the setup by reading the slides from pquerna's GeekSession's talk: http://journal.paul.querna.org/wp-content/uploads/2007/10/bl...