It doesn't matter how many coins are needed for destruction in his model, even 99.9% attack-proof currency would fall.  
It doesn't matter for NXT and other PoS currencies, because it's a ridiculous model.  

Short summary:
Each unit has a known, true value.  
Holders are willing to sell their coins at higher price than their real value.
An attacker has enough money to buy enough coins (using "true" valuation) to destroy the currency.  
Because he can do it, everyone sells his coins for nothing, because if he does buy the coins, anyone left holding will lose money. This causes the price to go to zero.
Therefore, it costs nothing to destroy any PoS currency.  

pure genius. let's sell nxt, everyone.