Rails doesn't have to be a one size fits all framework if you use it as a web delivery mechanism. That is the point of the Obvious Architecture http://obvious.retromocha.com/ You can see an example "twitter" app here: https://github.com/RetroMocha/obvious_status

In the case of my example you could swap out the /delivery/web/app.rb or delivery/api/app.rb out for rails no problem. You wouldn't need to change any of the code in /app or /external to do so whatsoever.

Just because DHH thinks you should write your code one way and you don't agree doesn't mean you have to throw rails away entirely to have a different or better structure. Rails might be opinionated, but that's just like their opinion man.