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I think PoW is only temporary for Etherum. Pretty sure they are working on something else but I don't have a link handy. It's prob on their blog though.
You are right. They want to switch to PoS. Vitalik said it will likely take 1 year to do the change. And we know from Bitcoin how difficult it is for PoW coins to do hard forks. Especially if the miners will loose 100% of their revenue.
So let's wait.
PoW coins is more expansive, cause each coin includes electricity bills. That's why they choise PoW - to make more money.