This attack requires a large % of a coin's stakeholders to be stupid enough to trust 'Pirate S+T'. Why don't you call your bank cryptodouble instead of Pirate S+T? I think cryptodouble is a catchier name, might get more suckers. In the accumulation phase, you are 100% operating a ponzi. How do you convince people to invest in the ponzi (I know, tell them it's not a ponzi, you instead intend to attack the currency)?

Explain why you can't do the same with a PoW coin? Just needs the added measure where you buy hashrate with your accumulated funds, but you would require much less funds. What % of bitcoin, what % of litecoin would it take to buy enough hashrate to attack? What % of a PoS coin would it take for you to attack that.

What happens if your attack doesn't reduce the value of the coin to zero? Does your attack merely consist of double spending?