Context: You have now moved xxx.example.com to a new domain and now are worried about the future sub-domains of the new domain.
I just went through Do subdomains help/hurt SEO?
I could find a relevant piece of information that could help in your case.
A highlighted quote from Vanessa Fox, an ex-Google employee, is this
Primary domains can pass a penalty to subdomains. Subdomains can’tpass a penalty to a main domain unless the main domain holds a clearrelation to the subdomain.
So, a good solution will be to host the moved website in the root domain (without www in case you are using).