[spankalee]

Chrome already supports the v0 Shadow DOM spec, and will soon support v1.

Edge(nee IE) and Firefox are committed to support and active in the standards discussions, and I believe allocating people to work on it, if not working on it already. Support across all the major browsers will arrive before we know it.

We also have polyfills for Shadow DOM and the other Web Components standards, and are updating them for the v1 spec: https://github.com/webcomponents/webcomponentsjs

The Shadow DOM polyfill is a bit slow, but soon it'll only be necessary on older browsers, so some properties might be able to adopt full Shadow DOM within the year.

If you use Polymer, we have a fast Shadow DOM-like shim called Shadey DOM, and you can pretty seamlessly opt-in to full Shadow DOM where available.