I don't see how a separate domain would solve the main issue here. If something on that separate domain was flagged, it would still affect all user content on that domain. If your business is about serving such user content, the main service of your business would be down, even though your main domain would still be up.
You are right, it would still affect all users. Until the pending PSL inclusion is complete, that is. But it now separates my own resources, such as the website and dashboard of statichost.eu from that.
A separate domain may not prevent users' conten from being blocked, but it may prevent blocking of the administrative interfaces. Which would help affected customers get their content and the service could more easily put a banner advising users of the situation, etc.