Ah PoS, the "Rich get richer" algorithm.

Ethereum's PoS implementation requires lock up of balances in stake accounts, so it removes any incentive to do transactions.

I believe that ETH PoS will calcify the economic strata, kill all transaction volume, and have the opposite of network effect.

PoS basically increases energy efficiency by decreasing the degree of randomness and skewing the dice in favor of stakeholders to the degree depending on their stakes (at the limit you'd have just one entity verifying all the transactions, a very energy efficient situation we have today with fiat). In general PoS looks like a reasonable trade-off, and we're to see whether it gets accepted.