80% of internet traffic is video and a good chunk of that is porn. If they are randomly sampling at IXs, they are wasting their time. Even if they were storing terabytes of data, there's no way that humans could cull it manually. They most likely search for key words related to terrorist groups and such. So, if you can invent a steganographic technique that hides your Tor circuits (or email, or whatever) in porn videos, you're good to go.