I think this is a great idea. One suggestion would be a process for nominating or voting on speakers from the HN community. If you send someone an email saying you've got 100 people who've said they would love to hear them do a podcast, that could be a great way to get them involved. It could be nice to have a mix of regulars who do well and guests (especially guests who have some relevance to a big story from that week).
I am more attracted to the idea that it’s simply based on HN activity, without a separate vote. Decide on the # of guests, say 2-3, go down the list of top stories, and reach out to the OP’s until there is a “quorum” of those who agree to participate.
I think a method like this would be more likely to expose lesser-known folks.
Thanks for working on this!