Earlier quoted context omitted.
DNS is very compact (a few hundred bytes a query), you're talking about maybe 10mbit of traffic tops: not a hard problem these days
It's not about size, it's about rate and introducing latency. Just the hijack itself is going to add DNS latency, which is monitored by any competent operations team. Expert operations teams, and I know of one, also monitor the BGP path to their public addresses (including nameservers) to detect things like the Youtube kerfluffle. Adding a conditional ("do I answer or do I proxy?") on every DNS query -- and there are…
Welcome to the world of recursive name servers, there is a lot of software out there that does exactly what you just mentioned, I fail to see what would be hard about making this change.