I've used react-rails as a way to use React components with low friction in rails views. However, its been a few years now since a significant percentage of rails developers have come to look at Rails as an API layer and use SPAs as the UI, regardless of what client-side framework you use.
Marketwise, Rails is on a long, slow decline. You should definitely broaden your horizons, even if Rails is going to be around for several years yet. You're probably going to see fewer "interesting" Rails projects come up, and a lot more legacy and "mature" applications. Elixir and Phoenix is where I'm putting my attention these days, but there's a lot of interesting work going on server-side these days as well.
Marketwise, Rails is on a long, slow decline. You should definitely broaden your horizons, even if Rails is going to be around for several years yet. You're probably going to see fewer "interesting" Rails projects come up, and a lot more legacy and "mature" applications. Elixir and Phoenix is where I'm putting my attention these days, but there's a lot of interesting work going on server-side these days as well.