Yea, I don't know a whole lot about Vanillacoin, but I'm pretty sure it's just taking a Bitcoin 0 conf transaction and using a locking mechanism (which may or may not have security issues) to just visually credit your account faster. The transactions all still have to be put in a block if you're using a blockchain system...you didn't just gain infinite TPS from nothing. All PoS systems that don't die will eventually switch to deterministic block validation anyway, thus making that 0 time thing irrelevant.
Vanillacoin does use a locking mechanism but it's not just visual. It's designed such that your coins are re-spendable as well. With regard to the mention of a potential security issue, there was a beta phase with a 2k vnl bounty (or somewhere around that amount) for anybody that was able to successfully exploit the network, which was not claimed. So while I wouldn't go so far as to say it's not possible, it hasn't happened yet.