Boris, if you don't mind me saying it, I am afraid you may be missing the point of this request. In Responsive Web Design, device capabilities are used in a high-level fashion to determine a class of the device: smartphone, tablet, desktop. There is no need for exact viewport state. All the image, css and javascript optimizations that need to happen on server-side can happen based on that information. Everything else (including things related to turning orientation or changing window size) are already covered by media queries in CSS3.
This is so much so that, in our discussion on the Firefox forum, it was suggested that maybe browsers just report device class: https://support.mozilla.org/en-US/questions/917322 This could be a great solution for all purposes, with one caveat: logic for which devices should belong to which category may change and whether browser vendors can adapt quicker or it's better if they provide raw data and let server developers adapt their server-side code, is debatable. Hope this clarifies the intent of the request/proposal. Thank you, Irakli
