I don't think the world should abandon HTML, nor break backwards compatibility across the HTML spec. The first cars drove on roads designed for horses, and horses are still around. At no time did we gather a committee and decree that horses were deprecated.
Taken to an extreme, "don't break backwards compatibility" has an insidious failure mode, which is "don't innovate." The car could not have come about without a willingness to break backwards compatibility with horse drawn carriages, plows, mills, hitching posts, etc.
The adoption of a radically new technology like this is voluntary, collaborative, and progressive. Provided it offers enough value to exceed the switching costs, there's no need to kill efforts or bury knowledge bases.
Taken to an extreme, "don't break backwards compatibility" has an insidious failure mode, which is "don't innovate." The car could not have come about without a willingness to break backwards compatibility with horse drawn carriages, plows, mills, hitching posts, etc.
The adoption of a radically new technology like this is voluntary, collaborative, and progressive. Provided it offers enough value to exceed the switching costs, there's no need to kill efforts or bury knowledge bases.