What stops that? (Both its widespread implementation and making it mandatory)

You mean what that protects against?

It provides the first part of my post, authenticating the packages.

The second part is cutting out misbehaving connections. On this case on the article, it would be trivial, and governments should be on the ISP shoulders making them make call everywhere and cutting some of their clients. But there are many attacks where the ISPs don't have enough information to act if they implement something like BCP38.