I Believe that eventually web components will storm the community. If you think Polymer is too "heavy" (and it does have also performance issues) I invite you to test slim.js (slimjs.com). Disclosure: I'm the author. And I welcome any web-components enthusiastic to PR and Join and I'm willing to share time and code with other libraries.
In terms of maturity - it is production ready. All evergreen browsers support it one way or the other, currently some requires a small polyfill (but it's temporary until all will complete implementation of the spec). It's working, It's easy to develop, reuse and I really believe that this territory will be the next thing in front-end development.