I love the idea of applications which exist in one file which you can run anywhere. I've been working towards this with my serverless platform; you can build complex data-driven apps with just one .html file and mostly declarative HTML markup (thanks to web-components which are loaded from a remote server). With modern browser features, you don't need a bundling system. Once you do away with it; a whole universe is opened up.

The ability to load .html files over the file:// protocol is a powerful, often neglected feature. In practice, it means you can double-click an HTML file and it runs an app in your browser instantly.