The worst they can do is exclude transactions from a block (which would quickly be noticed by stakeholders anyway) which would delay the confirmation of a transaction until the next honest delegate produces a block.
I thought you were also reading my thread because you posted in it. There is a worst they can do to a PoS coin (including DPOS):
- even 0.1% stake can attack the coin because block solutions are exclusive to some stake holder so the stake holder can delay transactions[1]
[1] Another scenario is DDoS attack other stake holders when their turn to mine a block, then jack up your transaction fees sky high when its your turn to mine a block.
Also you seem to not acknowledge that PoS coins can be shorted, so the risk of losing the value of the stake is not really valid argument.
I understood that PoS was motivated by the flaws in PoW. In my thread, I am working on trying to remove those flaws from PoW. We will have to see what emerges from that.