That's pretty neat. In general I think stuff like this is cool and works pretty well as a starter kit for simple CRUD apps if you don't already know Rails + JS, but like I said in my OP, once your app gets more complex, you hire some UX designers and you try to make your app more interactive, not having easy JS access makes it hard to do interesting things.

So could be useful for small projects but I wouldn't pick a solution like this for projects I would want to grow larger