My opinion might be kind of unstable. For my projects in the company I would choose write CSS alone or something like SASS or LESS. But for my personal projects I use inline styles with ClojureScript merge functions as well as inlined <style> elements to handle media queries and pseudo classes.
The problem inline styles does not fix is like handling media queries and pseudo classes. I see JSS showed a really interesting way to solve the problem and I would say: awesome!
Nowadays people treat the browser APIs like a virtual machine. Everything is compiled and we just need better compilers. Before JSS we use inline styles to write properties to Element.style directly. The drawback is it's only values. If we have 100 elements sharing the same styles, we have to write the styles for 100 times in all elements. Because we don't have variables like in JavaScript. However with the help of JSS, now we have basic support for variables. It's really interesting now JavaScript is compiled to JavaScript plus CSS!
I guess we can have more things like that in the future by treating the browser like a VM.