WHATWG is a cooperation between Apple, Google, Mozilla, Microsoft as far as control goes.
The Web is controlled by Google, Full Stop.
There is no "standards" there is Google. This has been shown more than a few times with things that Google Wanted, others opposes but some how the w3c always sides with google... hmmmm I wonder why that is
Nothing will replace it because 85ish Percent of the Browser Market is Chrome or Chromium Based. Chrome, Edge, Brave, <<insert name of your fav chrome clone here>>
I fully expect to see FireFox become chromium based with in the next 5 years.
While everyone was beating IE and Microsoft we surrendered the web to Google and Chrome
it will take a generation to win that back, if ever
Why do you expect Firefox to go Chromium-based? It seems a large part of Firefox's success is that it is an alternative to Google code.