RSS is really based on polling and that's not great. It also doesn't provide a lot/any analytics back to the content site to give attribution of content readership.
I think the idea is super interesting but it's not surprising that Google/Facebook and other ad networks made it less relevant.
The lack of analytics is a good thing. It's none of your business what I read, you already have it in your server logs that I've added your feed to my reader. I do not wish to feel like a tool and an asset of some company simply because I want to read an article.
A lot of sites have "solved" this nonissue by not including text in their feeds, instead only providing a link to the article on their site. A quick and easy way to make me unsubscribe immediately.
Can't you track who subscribes to the RSS feed, because of that polling you mentioned.
RSS is trivial to monetize, there are other reasons why Google/FB killed it such has having to educate people first, or not wanting to promote a free standard that would have not allowed them to monopolize the market
I think the idea is super interesting but it's not surprising that Google/Facebook and other ad networks made it less relevant.