Android's new developer verification rollout begins, sideloading changes are next
(www.androidauthority.com)
This is in no way a justification for what Google is doing, but they came to a "compromise" where you can still opt-in to being allowed to "sideload unverified apps" (read: install apps that didn't have to get approval from Google).
You have to enable it in the settings, and then you need to wait 24 hours before the setting is enabled. After that you can continue to run "unverified" apps