I like the idea of a minimalist, stripped back version of Google Reader, however, I think you'll struggle to get $20/year out of people with the amount of quality RSS readers you can get for free. Find an audience before you start building this thing and build it based on feedback of what they liked/disliked about Google Reader and the other RSS readers out there.
Yes, you might be right. Nothing's set in concrete, so if I do go ahead with this project, it's entirely possible I will change some of my ideas. Getting feedback is exactly what I'm here for. Thanks :-)