This seems very similar to what AngularJS or ReactJS offer with their templating systems. Is this just a matter or EmberJS catching up with those two or does this offer some new functionality (eg: performance)?
Handlebars has been the default templating system for EmberJS for awhile, but has not been optimal in some regards. The way I understand it is that HTMLBars is an evolution of Handlebars that increases performance under the hood, while barely changing the syntax in the front-end.
It sounds like it's a bit closer to React/Angular's approach. It still opts to pull your templates away from your view logic, but the fact that it uses DOM fragments and understands its own hierarchy make it a lot more like React when it comes do DOM manipulation.