I'm pretty uneasy about legal action against the subscribers themselves. If you can prove intent, maybe? But I'd argue many or even most don't realize they're doing anything illegal. These IPTV companies, in my experience, never advertise that it's illegal. It's just give us money for a lot of TV channels, just like a cable company does.
It's like those folks that sold bootleg DVDs out of their trenchcoats in Manhattan - the defense of "gosh, I never knew buying a just-released-in-theaters Hollywood blockbuster for $5 by some dude on the side of Broadway was illegal" was never going to fly.