I still think this is an acceptable footgun (?) to have. The expressiveness of downloading an image tag with a domain included outweighs potential miscommunication issues.

For example, if you're on a team and you have documentation containing commands, but your docker config is outdated, you can accidentally pull from docker's global public registry.

A welcome change IMO would be removing global registries entirely, since it just makes it easier to tell where your image is coming from (but I severely doubt docker would ever consider this since it makes it fractionally easier to use their services)

This is a huge stretch.

Even if you could configure a default registry to point at something besides docker.io a lot of people, I'd say the vast majority, wouldn't have bothered. So they'd still be in the same spot.

And it's not hard to just tag images. I don't have a single image pulling from docker.io at work. Takes two seconds to slap <company-repo>/ at the front of the image name.

Sadly doesn't help if you were using ECR in us-east-1 as your private registry. :(