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YouTube's next move might make it virtually impossible to block ads
(www.androidpolice.com)
This is a most excellent place for technology news and articles.
As long as the naming pattern is distinct from important domains you can still block it based on pattern matching. They need to obfuscate ad domains and other hosting domains the same way.
Creating subdomains is quite fast because the request goes right through when it's unknown to caches, it's updates when you reuse existing ones that causes trouble with lag.