[teknico]

> Has any serious blockchain successfully implemented PoS at this point?

Decred has, in production for months: <https://docs.decred.org/mining/proof-of-stake/>.

True, it's a hybrid Pow/PoS system, not a pure PoS one, which is indeed probably not workable: <https://docs.decred.org/research/hybrid-design/>.

[brulez]

It's not really clear to me how PoS is providing any security in Decred above that provided by the PoW.

If a single entity is able to get 51% of the hashrate why can't they effectively control which PoS tickets are selected?

Since the overall reward & transaction fees are distributed between both PoS & PoW, it seems to follow that at there will be fewer PoW miners resulting in less overall security vs. a pure PoW protocol.