Bitfury company did a research on PoW vs PoS [1] and their conclusion was "Pure proof of stake approaches pose substantial security threats that cannot be recre

Bitfury company did a research on PoW vs PoS [1] and their conclusion was "Pure proof of stake approaches pose substantial security threats that cannot be recreated in proof of work systems (including Bitcoin). These problems are inherent to proof of stake algorithms, as proof of stake consensus is not anchored in the physical world (cf. with hashing equipment in proof of work). That is why virtually all of currencies relying on proof of stake use additional mechanisms to address security issues." On top of that even Vitalik said "proof-of-stake systems are ultimately permanent nobilities where the members of the genesis block allocation always have the ultimate say. No matter what happens ten million blocks down the road, the genesis block members can always come together and launch an alternate fork with an alternate transaction history and have that fork take over." [2] [1] https://bitfury.com/content/downloads/pos-vs-pow-1.0.2.pdf https://bitfury.com/content/downloads/pos-vs-pow-1.0.2.pdf [2] https://blog.ethereum.org/2014/07/05/stake/ https://blog.ethereum.org/2014/07/05/stake/