This is exactly what Web Components are: a standardized, minimal, HTML-compatible, component model that's understood by the browser. It solves DOM encapsulation

This is exactly what Web Components are: a standardized, minimal, HTML-compatible, component model that's understood by the browser. It solves DOM encapsulation, style scoping, element lifecycle, and DOM composition. Frameworks and libraries can then build on top of that to provide templating, data-binding, additional lifecycle stages, and other helpers, which Polymer and X-Tags do.