[depr]

>The ad company can't pester their clients to make changes to the DNS on a regular basis.

Many DNS providers have APIs.

>And clients won't give control of their DNS to ad company, so automation is also not really possible.

Sure they will. Or they'll use another party that does it. They already add JS from the ad provider that does god knows what to all their pages, and give full control over their content to Cloudflare. So why wouldn't they give an ad provider API access to their DNS?