It scales fine for 99.9% of projects.
You can write functions in Python, JS or whatever other language you fancy.
Why do you need rails for the REST API?
Because i need production-ready auth, csrf. I want to add some cache layer with redis/memcached.
I want control over fields I pass to/from frontend.
I want to be able to handle multipart requests. And I want a decent logging system and debugger.
