AWS, GCP, Azure, DigitalOcean and even GitHub / GitLab all have private container registry offerings.
If your stack is on X provider, chances are you're going to use their private registry service instead of using the Docker Hub because you've gone all-in with that provider. That means private repos alone isn't enough to get folks to pay for Docker Hub.
Otherwise, I don't think it's practical to have docker itself as a commercial product.
- Every user gets 600 pulls per month for free.
- Pre/post pay per pull or buy a rate plan. Something like $100USD === 10,000 pulls on "pay-as-you-go" and prepay could reduce the cost per pull.
E.g. make base images for programming languages, systems, etc and guarantee security.
I think many small companies would like it a lot better if they got could externalize the cost of running docker images with all their dependencies.
I'd be pretty thrilled if Docker encouraged buildpack use. It would be a huge win for them.