If you look at the workflows for these changes, you'll notice that some of them are actually there to prevent you from doing stuff under duress.
Like it or not, if one wants security some freedom will need to be moved elsewhere.
And since the market is heading that way, the only thing we can do is form an android sandbox SIG and maintain a fork for enthusiasts.
Let's not be naive by pretending improving user security is the main purpose of that move.
May or may not be. It does significantly improve security.
I miss data to confirm any of this does significantly improve security.
Anecdata: I have yet to meet someone who have been targeted by unknowingly side-loading apps.
If they really want to improve security they can work on much more impactful changes. I know people having been scammed by ads proudly delivered by instagram and google. I read about malicious apps that somehow went through official store filtering.