From https://keepandroidopen.org/ :

"As of the date of this update, it exists only as a blog post and UI mockups. The community is being asked to accept a product announcement as a functional safeguard five months before the mandate takes effect."

"Until Google provides a shipping implementation that can be independently verified, our position remains unchanged: all apps from non-registered developers will be blocked once their lockdown goes into effect in September 2026."