We should see CEX.IO's statement and see what they are going to do.
Depending on how that unravels, it wouldn't be a bad idea to DDoS.
But DDoSing or Booting a service wouldn't really call anything in our favor. Bitcoin and other cryptos have a special feature, one that many currencies don't have. People aren't denied to mine, or have it. Nobody can confiscate it.
If we DDoS CEX/GHash just because they're mining, and yes, they might be getting close to 51%, that's still not a excuse to say, "Yeah. They're getting close to doing something dangerous. Let's make a exception." Because if that was the case, I don't think Bitcoin would be were it is now.