Caching is definitely important for front end tooling, but it depends on which tooling you're having perform the job. It is also generally considered a deployment worry. Cache busting can be implemented in various ways-- by using a templating language (ex. ERB), by using a build tool like grunt/gulp, by using you JS bundler, or by using your module resolver (in the case that the bundler and resolver are not the same entity).

JSPM just doesn't take a built-in stance on it (as of now, as I noted there is a ticket to get it included), but it certainly is configurable enough to allow you to add cache busting (by changing the loader). Not trying to apologize for JSPM -- it would certainly be better if they had some sort of cache busting option that was easily available and obvious.

I think the thought here is that when you're ready to push to production, and you build your actual bundle, you name that file whatever you need to to bust caches.