Well you can already do that with Canvas, and as you said things like Doom or Quake have already done so, but you are basically ignoring the entire DOM and JUST

Well you can already do that with Canvas, and as you said things like Doom or Quake have already done so, but you are basically ignoring the entire DOM and JUST using the canvas as a framebuffer. And like you said Qt already knows that (somewhat, there have been tech demos showing this but no real applications built on it), but it still means that YOUR APPLICATION must handle all of that, meaning at best you are downloading all the code for all of that at runtime, and at worst you just won't handle it because most people don't want to spend the time.