This is such a neat idea, and you get the gist of it from just the screenshot. I wonder what kinds of 'integration' you could do (clipboard, opening links, drag-and-drop, etc). I could see this as an educational tool for doing development on a Chromebook, because of the (emulated) terminal + filesystem.
Indeed the modern Web API's can do all that and more. One of my favorites is dragging out of the browser onto the desktop. Another is ctrl+c'ing a file on the real desktop and then ctrl+v'ing it into the "fake" one. Some super powers sadly are locked away in the need for a PWA, but I think they could one day just be part of what any site can do.
Technically it's not developer mode , it's just a regular feature of the OS. "Developer Mode" on ChromeOS is when you remove boot verification for ChromeOS itself.
