Is Proof of Work is going to lose popularity compared to Proof of Stake? Ethereum is going to PoS. 
Is there going to be a lot of hash (computational) power idle because of shifting to PoS?
Where that power be used then? Will it address such decentralized computing projects as Golem, Storj, Sia, etc?
Is there going to be a lot of hash (computational) power idle because of shifting to PoS?
Where that power be used then? Will it address such decentralized computing projects as Golem, Storj, Sia, etc?
I don't think that there will be "idle" power. There are so many altcoins and bitcoin mining opportunities out there in the market that it's not an issue for a miner to switch between coins extremely easily. Think of it as mining hashpower being very elastic supply.
Is PoW going to lose popularity though? I don't think so, until BTC switches to PoS at least.
And I don't see any reason for BTC to do so given the fact that it's working as is, and PoW is doing its job well to secure the network.