Proof of stake is permissioned by coins, an internal, permissioned, and already owned resource.
You cannot gain tokens without someone choosing to give up those coins - a form of permission. Permission can also be thought of as an infinite barrier to entry.
PoW forces giving up control through both permissionless to enter mining via EXTERNAL
permissionless
resources and unforgeable costliness for the miners.
Without unforgeable costliness there's no reason to ever give up control in PoS.
In fact, staking quite literally incentivizes keeping control by rewarding those in control with more coins and control in perpetuity at no cost - the incentives on PoS are completely backwards from decentralizing control.
Since no mechanism forces control to be permissionlessly distributed to others, parties in control cannot be considered independent parties nor can control be considered decentralized.
PoS solves nothing that's relevant to permissionless decentralized networks.
In the following years we'll be seeing proof of stake being implemented
It has been implemented since 2014 but it doesn't meet criteria for a permissionless network. There's nothing new about implementing permissioned networks.
You could try to replace proof of work with proof of bitcoin burn
(not well studied) on blockchains other than Bitcoin, but there's no known replacement for proof of work for Bitcoin right now.
PoS has been considered and studied since then many times since then and dismissed repeatedly for irrelevance to decentralized permissionless technology, examples: