Small problem was the way feeds worked in practice is you had various services caching the source feed and consolidating everything for its users like Reader and Feedly and others. Multiple startups around this.

Even the injected ads idea was tried with companies like FeedBurner, later acquired by google.

Not that much different from any other form of content aggregation. Web links posted to HN or Reddit also either strip out individualized links or conflate everything together under the same link. There are plenty of solutions to this.

If you're generating feeds on the fly with tracking metadata based on the requester, you can identify aggregators, and treat them equivalently to social media platforms where users circulate normal web links. You still get click-throughs to the underlying content from the end users, and you'll know the aggregator was the referrer.

Many podcasts use direct ad injection using metadata from the request to the enclosure link -- that seems to work well enough, and seems like the sort of thing that could be used for other content than just audio and video.