The author doesn't write "PHP belongs in the past".
PHP is still great and could benefit this CMS, which reminds me a lot of Kirby CMS. Kirby has the same ambition "get our of your way" and everything is static files, no database if you don't want one. Except Kirby has the added benefit of PHP and optional databases, and easier setup for people who aren't fans of the letters "npm".
But replacing PHP with server-side JS is not the kind of progress that I'm into.
Anyway: congrats on the release!