I could define the next points why we have to migrate:

• Decrease build time of our application. (It was the main cause).
• Also jspm install takes much more time than npm install.
• Many config files for SystemJS and JSPM. For Webpack you can use just one main config file, and you can use some separate config files for specific builds using inheritance and merge them.

We mostly use rollup to publish package onto NPM. For most all other use cases, we use the Meteor build tool (probably 99% of the time) for publishing packages. If you're using Node on FHIR you probably won't need to know rollup, unless you are somehow working on helping us publish front end user interface components using FHIR. That being said, we have been migrating away from Atmosphere package manager towards NPM. As we continue to migrate away, we may publish other NPM packages using rollup.