Wait, fly.io is a Rails shop?

(At any rate, they employ Chris McCord, the creator of Phoenix, and have spent considerable resources pushing Phoenix. So it's clear that they aren't beholden to any one language or ecosystem.)

I think we have more Rust and Go than Ruby at this point. Probably slightly less Elixir.

For better or worse we're not really fixated on one language.

He explains the use case why you need a RP framework in your language of choice not his desire at fly.io (I guess :))