There's nothing that would prohibit maintaining a Backbone or Knockout app (or just one written with a bunch of non-spaghetti-code jQuery) today, and it's hard to say that any other choice for writing a piece of software with a GUI would have fared better. Why do you think that using React will have a worse result than that?
I think that of the kinds of tools people are using to make web applications in 2017, React and Rails are probably in the more conservative, most likely to be maintainable in 10 years category. (I wouldn't believe this about Rails except it's been so popular for the past 10 years.)
> There's nothing that would prohibit maintaining a Backbone or Knockout app (or just one written with a bunch of non-spaghetti-code jQuery) today
Well that kind of depends, I still have stuff in production with knockout and for some stuff I still use it but it's not just a matter of the framework/library it's the ancillary tooling.
We went through grunt, gulp, browserify and webpack fairly quickly, we could have stayed with any of them but no-one else did, if you stand still you end up been left miles behind when you eventually do want to move on.
The dozens of different bits approach has a lot of advantages but it has some severe downsides as well.
Modern JS is a bit of a red queen problem, you have to constantly adapt your codebases just to stay even on a 5-10 basis.
It's a problem in my world (enterprise LoB stuff in the browser), you want to be somewhat conservative while still be able to have some assurance of long term viability and some of the nice toys.
My approach has been to trade off dependencies as much as possible, I moved to TypeScript for a lot of stuff since it emits good JS so if it ever did go away I could just output the most recent JS and base from that (and I doubt TypeScript is going away in the next few years, MS has invested heavily in it as a platform for internal stuff).
Meanwhile over on the other side of things I recently ran something that was written in 'pure' Java 1.2 on the modern VM with not as many issues as you'd think (that platform is 20 years old).
I recently inherited a large enterprise system that is classic jQuery/no framework, it 'works' on a modern browser but it's an unholy unstructured mess and getting any kind of iteration velocity on it is a complete pain and that was written in over a few years finishing two years ago.
The developers just hadn't adapted to the modern landscape well at all and their momentum was terrible and getting worse.
I think that of the kinds of tools people are using to make web applications in 2017, React and Rails are probably in the more conservative, most likely to be maintainable in 10 years category. (I wouldn't believe this about Rails except it's been so popular for the past 10 years.)