Compared to 2.0, Polymer 3.0 is the biggest change in the history of the project. Polymer has been using Bower and HTML Imports to manage dependencies since early days: Bower installs dependencies and HTML Imports is responsible for loading them. Version 3.0 will use ES Modules instead of HTML import and will migrate Bower to npm.
In the recently updated Roadmap, the Polymer development team stated that in the 3.0 release, Polymer Elements will also be converted to ES modules and distributed via npm as core libraries. The Polymer CLI and related tools will also be updated to support the development, testing, and deployment of projects composed of ES modules.
Of course, despite this great change, the development team stated that it will make the transition as seamless as possible. The Polymer 3.0 API will be basically the same as the 2.X API. At the same time, an upgrade tool (polymer-modulizer) will also be provided, which will automatically handle the conversion work of most 2.x-based Element and applications.
