To clarify, the loading case I mentioned is related to single page apps. The server isn't the one rendering the page when the loading indicator pops up, that's

To clarify, the loading case I mentioned is related to single page apps. The server isn't the one rendering the page when the loading indicator pops up, that's entirely a client side render ("isomorphic" being the ability to fully render on client or server side with the same codebase). The server doesn't need to stream a page with a loading indicator in the HTML. Being able to stream part of the app while data is loading (like the header) does seem like an interesting case, but it would only matter for the initial page load in an isomorphic SPA.