I'm pretty much a JS novice and learned quite a bit about Backbone in less than a week. I've tried React and Angular. Neither stuck. However, I'm sure I could've learned enough to use either for the project I was working on. I could probably say the same about other JS frameworks.

I rolled with Backbone because it was in core WP and things like media views already relied on it.

In the WP community, we need more documentation on the JS included in core. The PHP in WP has always been well-documented, both in the code and on the Web. The same cannot be said for the JS (though inline docs are improved today).

What we seem to be missing, regardless of the JS framework used, is WP folks who are teaching others how to build with JS.