The static assets are actually served by nginx. In cases where some page data is dynamically generated by Rails, it's nice to keep both pieces of code together in a mono-repo. That said, when I recently extracted a Backbone app from the Rails codebase (retrofitted Grunt.js), I decided to ditch the public/symlink approach and split the app over 2 subdomains. What I find now is that I like the mono-repo approach, and would be fine with cramming both codebases together, while having granular and global deployment scripts.
I actually do this: I ended up leveraging sprockets to get some environment interpolation (like API locations) and easy preprocessing languages (e.g. coffeescript). Also, by doing this, I don't have to make everything single-page. I can build one off pages if I want to (not that it happens much, but, still). Also I get some nice bits for logging, metric agents integrate easily, etc. I realize I didn't need it, but, there really wasn't a down side to using it, except for that some views ended up a little fragmented when using angular templates in public/ versus actual views... Even then, it was a decent learning experience and I'd probably do it again just for the interpolation and sprockets asset building.
