It's good to be looking for holes in the #Bitcoin and PoW system. But I don't see it. We are stretching. EVEN if the pools of miners become more concentrated, LONG before their is a problem there will be a LOT of discussion.

The miners have no incentive to corrupt the network. EVEN if miners get to a 51% attack (which we will know long before it happens) there will be 1000 working on fixing the problem due to their OWN interests. Let's not forget the Nodes - which I run, along with at least 20,000 others.

The system will only grow stronger against attacks, as it has done sine the block size wars. 

 This is about things like OFAC compliance. Currently, with the small number of pools, would-be censors have a short list of people to squeeze. With SV2, those censors would have to put the pressure on individual miners everywhere.

It’s the difference between Napster and BitTorrent.