Just because on most modern hardware file I/O has millisecond latency and feels synchronous doesn't mean it is synchronous. It might feel like overkill to use Observables instead of Promises and I/O event loops or even thread-blocking faux synchronous file system calls, but there is still an asynchronous world there where it can be nice to have the full power of Observables. To be fair, my love affair with Observables started in C# in "backend" applications, so that's always been the natural fit for me and frontend and UI work has been the "side hustle" of taking stuff that I love in the backend side of the house and putting it to even more use.

I'm calling my view engine Butterfloat, and I only just finished the first documentation pass, so be gentle, but feedback is very welcome: https://github.com/WorldMaker/butterfloat