I did give JSPM a try. Actually, a lot of tries. I REALLY wanted it to work. As i mentioned in the post as well as in multiple comments, I really wanted it to work, but incremental builds plus hot reloads, vs client side compilation meant several orders of magnitude of difference in a medium sized code base. It was simply not viable. Having to do code splitting and lazy loading for development purposes in situations where it was not necessary for users was just a big problem.
I could list out all of the pretty critical scenarios JSPM didn’t handle properly as an application grow in size and complexity, but that would be a blog post in itself :) Rollup is extremely limited too at this point.