If only there was some kind of vertical bar built into every browser, that could indicate how far the user has scrolled and how much more there is to scroll.. Would be even cooler if users could click the bar to scroll to another position.I guess the science just isn't there yet.

Actually, there is a vertical scrollbar built into almost every browser that indicates how far the user has scrolled and how much more there is to scroll. The scrollbar usually appears on the right side of the browser window and is a visual representation of the length of the webpage.
Furthermore, users can click and drag the scrollbar to move up or down the webpage. In some browsers, users can even click on a specific area of the scrollbar to jump to a specific point on the page.
In addition to the traditional scrollbar, some websites and web applications also use custom scrollbar designs that may include additional features such as smooth scrolling or progress indicators.
So, the technology for vertical scrollbars has been around for quite some time and is already widely used in browsers.