Whether its PoW or PoS, they both are same way of climbing the same mountain. As PoW is centralized along miners that can afford expensive mining equipment and electricity bills, in PoS those who can stake huge amount of coins will grab the major share of mining.
That's also what I am starting to think lately. Why waste so much electricity when you can just have the same security with PoS? If the issue is centralization, there it is already here with the miners. One way or another there will always somebody/some entity will control the majority of the chain. You can't really prevent this.