Yes!
> Going forward, we will show multiple examples of prefixes. A user looking to add a custom domain will see a variety of example zones when they visit the page, and the examples will cycle each time they open the configuration page. We want to convey that they have options in choosing the name, and we show them a variety of sample options. Our hope is that this will prompt customers to pick their own names, and if they do rely on our examples then those are now spread over a large list of examples.
No! They were so close and yet it sounds like they've still missed the point. The issue is that users don't understand the "why" behind the prefix. Just randomizing the prefix that they're shown does nothing to change that.
IMO, a better solution would be. 1. The shortest possible explanation under the field of why you shouldn't use "someprefix". 2. Prevent users from using "someprefix" as the prefix and show them the warning again. By eliminating the default option as an option, you force your users to leave auto-pilot mode and actually consider their choice.