I would pay for this. While Rails development stuff is useful, I feel like there are a _lot_ of resources out there for it on the web. This isn't so true for Mac development in particular, at least to my knowledge.
I'm thinking about doing a MacRuby course this summer. That's at least in your direction.
You are going to have a Ruby focus, then?
Most of the people involved are Ruby people, but we'll look to bring in new authors as the site grows.