It seems to me that HTML5 needs an endpoint to handle AJAX and COMET-style loading. Fewer and fewer web pages actually use reloads all the time, content is just retrieved and switched out with JavaScript.
Loading bars are necessary, and they certainly aren't new. The browsers just need to be updated.
Since we're seeing a lot more of these kind of single-page apps, it might be wise for the browser vendors to implement a JS API to trigger the loading indicator on-demand, so it would show the loading UI that users are already familiar with. Has there been any movement on this?
For browsers that also show a loading progress bar (like Safari), it could also allow the page to set a precent loaded value. XMLHttpRequest2 supports progress monitoring.
Loading bars are necessary, and they certainly aren't new. The browsers just need to be updated.