Selenium is working with browser vendors to create the WebDriver BiDirectional Protocol as a means to provide a stable, cross-browser API that uses the bidirectional functionality useful for both browser automation generally and testing specifically. Before now, users seeking this functionality have had to rely on the Chrome DevTools Protocol, with all of its frustrations and limitations.
The traditional webdriver model of strict request/response commands will be supplemented with the ability to stream events from the user agent to the controlling software via WebSockets, better matching the evented nature of the browser DOM.