" Just be sure to set high TTL for the records so your DNS server does not collapse under the enormous volume."

The attacker, noticing your round-robin approach, decides to drop the DNS server and then only has one host to deal with.

There are a lot of weak points that can be attacked. Certain sites will have features that can be taken advantage of. If you have a long timeout/keepalive, the attacker could launch lots of quick requests with no proper tear-down. If you have a zillion servers setup like this - perhaps they can take out a major link before the traffic even gets to you.

I also don't think this is a new approach - unfortunately it is much harder to stop attacks than to create various approaches. The number of compromised machines is just too high - that is the ultimate solution.