Build an approval process for Gateways before they become Active on a tenant. The approval process would be manged by the Power BI Admin. This approval process could be a feature the Power BI Admin can enable / disable, defaulting to disabled to retrain backward compatibility. Current reality allows anyone with a Pro License to push any internal data they have access too to the service. With the right permission they can then push this data public without restrictions. This feature is a must have in an Enterprise concerned about how data is used / managed. Just because some has access to a data source doesn't mean Data Admin wan't this source to become publicly available via Power BI Service.