I've checked Shepherd and love the idea! Did you interview all of those authors? :o
btw, have you thought of doing podcasts too?
I've played with the idea as it is hard sometimes to find great ones, both newsletters and podcats in niches, it is something I've thought about with Shepherd (but don't have time for a while).
Yes, actually, I did! I love podcasts and I think that this format would be a perfect fit.
Though I was hoping to explore this idea after readsom will get enough traction - so it would be worth it:)
You could do a feature of every newsletter author to try to get publicity with each one.