The way users interact with our site is increasingly diverging from the classical "page view" model. As an example, hovercards and similar functionality in the apps is actually showing a good part of a linked page in a preview, but using this preview does not result in a navigation away from the original page. Similarly, MediaViewer is showing images and information very similar to image pages, without loading the image description page. Videos and interactive content can engage users deeply, but again don't cause navigation events that would count as a "page view".
To side-step fruitless discussions about which events should count as a "view", I think that we should add a new metric to better capture page view and non-pageview interactions likewise: Time on Site.
I think we can collect such information in anonymous form, without a need for session tracking. A recent article by Ilya Grigorik shows how to use the W3C visibility API to fire events when a page is hidden by navigating away, switching tabs or apps. By hooking into those events, we should be able to send a small beacon request containing the time spent between page load and -hide.