Also, how long does your actual bundle time take? For small projects, I actually get away with just triggering the bundle command when appropriate files in the project change. I highly doubt it would work for you, but if you're spending 10 seconds waiting for stuff to come in over the network, and your bundle command runs in 5, you could just do that instead, and actually work with the bundled code (and generated source map)
Looks like I'm not the only one who thinks it's sometimes a good idea: https://60devs.com/optimizing--default-jspm-workflow-with-gu...