I do fear for all these youtube alternative app developers. If I was building them, no way am I handing over my personal ID to Google. They would leverage that almost immediately.

They will continue to not verify their identity with Google, the same as they do now. This is where the new unknown sources installation flow comes in. In the future, their users on Google Android devices will have to enable developer mode in order to install these apps. On the plus side, this setting will persist when users migrate to new devices, unlike now. On the minus side, there is no reason this should require enabling developer mode. This is what people should be complaining about.