Let's not forget Grape either: https://github.com/intridea/grape

You could see this move towards JSON APIs way back in 2012 as I suggested here: http://paulbjensen.co.uk/posts/2012/07/11/thoughts-on-rails-....

Some poo-pooed the notion, but you can clearly see that the popularity of realtime frameworks and the way that apps are built client-side heavy is pulling Rails in this direction.

Performance is still the key factor here, and I suspect that's half the reason why you've got some people who espoused Ruby in the past now playing with other languages beginning with Ru, but that have a much less friendly syntax compared to Ruby.

Some welcome changes though nonetheless, especially on the WebSockets front.