Thanks for your response! Definitely agree ad tech needs to improve in order to hit $1b. One way that could happen is networks that aggregate lots of smaller publishers, bundle the audience together, and sell traffic at scale to advertisers. Another is that a platform could come along (like, in an alternate universe where they had good product execution, Stitcher) and sell audio ads to listeners directly, with some sort of rev share to content creator (or not).
Either way, in order to do a deal with the big spenders and get them to shift dollars from TV, you need to sell them audience in bulk.