Ember FastBoot is a cool project. Glad to see they are close to production ready.
Tom mentions they are leveraging App Cache, which is notoriously hard to work with and will likely be deprecated. That's the scrappy stuff they are doing, comparing it to how jQuery once made the DOM easier to work with.
If a future Ember release was able to abstract the client-side caching between App Cache and ServiceWorker and automatically "upgrade" my apps to use ServiceWorker when available, that's a big win. I'm not sure that's possible though...
