RFC: Engines

[RFC](https://github.com/tomdale/rfcs/blob/master/active/0000-engines.md)
How's that HTML-compliant tags align with (presumably) [allowing tags](https://github.com/stefanpenner/ember-cli/blob/master/blueprints/component/index.js#L40-L44) with slashes after the Handlebars 2.0 update?