So why is this not already happening?
Partly because there are no decentralized PoS coins that are alive.
The developers of PoS coins either sign blocks as valid (e.g., Peercoin) or create new "updates" with checkpoints (e.g., Nxt). In other words, they solve the history-rewrite problem by acting as a central authority.
If you know how to kill it why don't you do so?
https://yourlogicalfallacyis.com/burden-of-proofI said that no one had proved that the "nothing-at-stake" problem can be solved--I never said that it was unsolvable (although this is my opinion). Until it can be proved to be impossible, I must accept that it may be possible (and I do).
Honest questions..
Considering that you wrote "if you know how to kill it," when I never made that claim, and then employed a logical fallacy "why don't you do so?" (burden of proof), I disagree: they weren't really honest questions.
I don't pay much attention to what you write because I don't have the time - so it was an honest question.
It is good that this dialogue is being done and I am not biased in favor of NXT although I was one of the early adopters.
Trust me, I would prefer to be 10000% sure that NXT is indeed robust and I prefer people who bring up possible vulnerabilities rather than shills.
That said I could try and find a good bounty for you if you help find a decentralised solution to N@S...