I think this speaks of a larger trend with the Rails platform. What I mean is that it's now a mature platform and Railscasts have covered a lot of ground. My guess is part of the burnout Ryan is experiencing is due to a dwindling amount of material to cover without venturing outside of the platform, which he has been doing (and is welcome).

While I love Rails and Ruby (and learned a ton from Railscasts), the future of the web is building a separate RESTful API + separate static JavaScript browser app + any other devices like mobile, Glass, etc (opposed to nesting client-side JS apps under assets).

Edit: In response to the downvotes, let me clarify: I think Ryan is running out of topics in the context of Rails. He's a great teacher and I'm a paid pro subscriber.