>>1049871 (OP)
There are, right now, advertisements on podcasts. The ad is just audio interspersed in the middle of the podcast. There is no way to track whether is got listened to, how many people listened to it, whether there was "engagement", or anything else. The only metric the advertiser has is if their sales went up afterwards. Podcasts are also extremely decentralized. They use an open protocol (RSS) which anyone can host on their servers. As podcasts are becoming more popular they are swiftly becoming more centralized. Spotify bought some podcast company and made them spotify exclusive. I imagine they'll start offering incentives to podcast makers to move to their platform, maybe offering money like epic is.