So one attack vector is forging with timestamps artifiically advanced by almost 15 secs,
and having many nodes disagree on whether the new block is valid or not...
and having many nodes disagree on whether the new block is valid or not...
You need coins to forge, a lot of them, that's why it's called Proof-of-Stake
Why would you destroy your own investment if you spent billions of USD to buy up 51% of coins (or 90% of coins when TF is implemented)?