I'm curious to understand, how necessary will Ether be after the Ethereum network moves to Proof of Stake?
I guess stake holders will be rewarded with Ether for voting on the correct next block. Would love to hear your thoughts on this.
It is absolutely necessary, because any form of Proof of ... requires those who secure the network to be rewarded. The goal of any consensus form is to attract many nodes to a game like roulette. The winner can confirm the authenticity of the last block and wins a reward. Because the winners are randomly selected we say that with many confirmations we are approaching certainty that the block is not tricked with double spends etc. What is not necessary is the creation of new crypto once the system has settled. This is because the miners can be rewarded with the transaction fees.
It's necessary, because the miners or "validators" put some money on stake. Here is a description of the finality circle by V Butterin, which gives some good explaination of how it works :