Bundles might make sense, but one large blob that couldn't be parsed until it was finished loading would probably be a big step backward for responsiveness. Parallel downloads also help speed things up.

Another interesting idea for JS-heavy sites is server-side pre rendering (yes, having the server generate HTML like the good old bad days) like Ember FastBoot http://tomdale.net/2015/02/youre-missing-the-point-of-server...