Elixir and Phoenix are excellent, and you'll recognize many of the same concepts in these. The communities are excellent as well, and welcoming to newcomers.
They're fantastic and I hope the future is bright for them but I've had to pick Rails for a few projects over the last few months because the library support is so much more established. The more I get to use Phoenix, the more I am convinced it is the most well designed web framework there is, so I hope to use it a lot going forward.
It took me a couple of hours to build my first demo with it, have a look: https://youtu.be/tTPH4DyUaUk
and I didn't have to write any JavaScript for it.
Elixir/Erlang's emphasis on uptime/fault-tolerance/scalability/concurrency (admittedly at the cost of performance and the abstraction of a VM) is perfectly suited to web/mobile use-cases.
On paper, Pheonix should be the default choice for large and small web/mobile MVC applications. I think the question of if that becomes the case is directly tied to adoption of Elixir.
The performance comparison matters if you start comparing nginx, and maybe even the Go/Rust frameworks, but it absolutely blows Rails out of the water for performance without sacrificing any of the high-level abstraction goodness that makes Rails appealing. No reason not to move to Elixir unless you cant hack functional programming IMO
I've found that Elixir & Phoenix are the right abstraction of Rails-like productivity but "enterprise" reliability and scalabiliy. You get real-time functionality out of the box (dosen't feel cobbled together like Rails channels and blows anything Node out of the water). And with LiveWiew coming soon, it's going to be even quicker to build modern interactive experiences.
