Browsers like Chrome already allow you to install websites that support it to your computer as a desktop app, and a page can already fill itself with a canvas e

Browsers like Chrome already allow you to install websites that support it to your computer as a desktop app, and a page can already fill itself with a canvas element to allow itself to be programmatically in charge of all the pixels in it. What you describe sounds like a more limited version of what we already have today, other than the suggestion that this should be a responsibility of the OS.