Comment by bapak

I don't see a problem with what you're saying at all. For reference, you can already have HTML in SVG in HTML in SVG.

If you have a canvas-first page, where do you store the title? Right, in <title>, so

    <!doctype html>
    <title>My canvas site</title>
    <canvas style="fill all">

In reality they should really just allow content in the canvas element and call it a day:

    <canvas type="html">
        <h1>Canvassing</h1>
    </canvas>