Perhaps off-topic but I was quite fond of Prismatic. Is there a good replacement out there you've found?
No, unfortunately. I haven't really searched much. My patience for trying out new tools isn't all that high. The only two I've really used have been NetNewsWire (which I stopped using I think back around the time NewsGator acquired it) and Prismatic, which I never really found useful. The closest thing I use now is HN. I think likely the next tool I'll use in this space is roll-my-own as the author has or some app that provides the building blocks or plugin architecture for customization along those lines.
One aspect the author touched on is "I'd like to be suprised by relevant things that I don't know about." It's not immediately clear how to discover serendipitously items that are outside of the things you're already interested in, and therefore would already be in your feed. This is an area I'd like to know more about.
I'm also really keen on someone taking the time to automate curation of their own feed. One can still fall prey to the more negative aspects of Daily Me[1], but at least you're better aware of what's going into producing the feed you're reading and have the tools to update it if you find it's not serving your best interests.
[0]: https://en.wikipedia.org/wiki/Prismatic_(app)
[1]: https://en.wikipedia.org/wiki/Daily_Me