These proposals do not address the fundamental concerns in the document that gmaxwell posted. They do add a fair bit of complexity, making them hard to analyze (and making a concrete attack too intricate to describe). IIRC Vitalik has backed away from these proposals because they do not provide the security benefits he originally thought they did.

It's worth noting that by writing a well-defined security model and working toward it, it is possible to create a "working" PoS which is only broken when the assumptions of the security model are violated. If one were to do this, it would then be easy to point out how the security model is not applicable to the real world. But Vitalik's posts --- and no PoS writeups that I'm aware of --- actually do this.