The gist of it was that the sourcebook would cover material & locations that Jim Butcher isn't planning to hit - but he will have input into its direction and sign off on it, so I suppose it'll expand the canon 'verse.
I'm really curious to see if they carry on the writing-from-Billy-Bob-and-Harry's POV thing or if it'll be from another principal in the Dresdenverse, say someone who is more involved with the Paranet and lives in LA...
Good podcast in general, and I got to learn a lot about Apocalypse World as well (now there's an interesting sounding game to look at and pick up). Other noteworthy Evil Hat news was that they're now distributing Diaspora, which is a pretty awesome flavour of FATE aimed at hard sci-fi.