The only thing being over international waters will do is make them less likely to fall on people in the EU, Asia, or the Americas when they're jammed or shot down.
ACTA has been signed into law in many places. That means anybody who is signatory to that bill can act independently to enforce it over international spaces. If Pirate Bay were a government, it might be different. But even if they were, they'd still need the resources to enforce their own interests. As in their own nukes, army, navy, or air force - or via a treaty with willing ally that has them.
Simple truth is might still makes right
on this sorry planet. Powerful countries routinely flaunt international law without fear of being brought to book. And when it comes to getting heavy about something half the world already thinks is illegal, it's not a tough PR sell either.
In Pirate Bay's case, I'd suggest they take a look back to the 70s when a few pirate radio stations were being set up on ships just outside the territorial limit and broadcasting radio into the United States.
The first day they started broadcasting, the US Coast Guard went out, seized the ships (in international waters), took the crews into custody, and that was the end of it. Nobody lifted a finger to help the station operators. And this was back in the anti-establishment Viet Nam protest era when the US government didn't dare try one tenth the things they can get away with today.
I think the main reasons there's been so little official concern over this plan are:
1) It's ultimately unworkable and unsustainable.
2) It's expensive compared to a straight online approach.
3) It will tie up people with a 'science fair project' who'd probably be more successful doing end runs around web security and monitoring
4) Even if it does fly, it will be fairly easy to intercept and destroy. Might even make a good training exercise for fighter pilots thereby giving governments the opportunity to save some money on their own target drones.
Dunno. Sounds like a pretty dumb idea to me even if it is a cool concept.