I don't understand why people say this. At any given minute, aren't 1/n caches about to expire? So a few people will be hit immediately, and the number will grow from there.
With google.com and many other big players having a TTL of 300s, that's not a long time.
They are not planning to attack Google's name servers, just the root servers that hold the delegations for the TLDs.
The .com delegation is set to cache for 48 hours, for example. This simply will not work at all.