We're working hard to better communicate the core team's goals and roadmap. Today we're excited to announce a new repository - Polymer/project - where we'll keep all meta-information about the project itself. This includes a Roadmap, Code of Conduct, and Contributing Guide.
We decided on a repository rather than Wiki primarily to open up broader discussion about the project structure and direction. The Polymer project consists of many different repos, of which Polymer/polymer is only a small part. It can sometimes be hard to know where on Github these kinds of collaborative, project-level discussions can take place.
The Polymer/project repo will be a living document, and continue to evolve - so feel free to star the repo to follow changes as they happen. And like any of the Polymer project repos - PR's welcome!