This is a nearly pure market system, driven by economic incentives. Cryptocurrency mining is the best and highest use for the scarce resource of energy. Once it becomes unprofitable to mine, then the hash rate will stabilize and the energy will be used for better purposes. Marginal producers of hash rate will be priced out of the market.
Otherwise the whole thing sounds like the paperclip maximizer justifying its actions: "But if I burn this forest, we will have even more paperclips!"
Security is ensured by the economic incentives baked into the protocol. Security is the by-product of economically selfish behavior.
Proof of Stake, though, worries me. It's a very "the rich get richer" solution trying to prevent the rich getting richer. Less electricity, sure, but it feels like it deepens the economic wedge between classes. If you stake 1 coin and I stake 100 coins and there's a 10% reward, after payout you'll have 1.1 and I'll have 110. How is that decentralizing? And you can't put tiers in the system because people will just install a thousand wallets/nodes and split their coins until they fall into the highest paying bracket.
I really like what the Monero folks are doing. They announced that they'll be making small changes to their PoW algorithm a few times per year in order to deter ASICs (no point to spending time and money on a super specialized machine that will be worthless in 2 months). It doesn't deter GPU mining too much, though I'd imagine that it's more of a hassle keeping a swarm or systems up to date than one rig. Ideally, they would release tweaks that reduce GPU efficiency, like highly serialized computations with lower difficulty (so the payout is similar).
And then you have Gridcoin, Curecoin, and the AI focused coins that give something back to the world, forcing a charitable donation. It's a shame that they aren't more popular/valuable. They're kneecapped by academia's schizoid relationship with computing in too many ways, but seem to have good teams and communities behind them.
My amateur opinion is that the flexibility of shown by Monero (changing their PoW algorithm) should be standard for all coins, as should the usefulness of work, like Gridcoin and Curecoin (not just 'securing the network'). Maybe something like a carbon tax, where exchanging the currency carries a contract to provide some proportional amount of work in a scientific project. Use a reverse Proof of Stake with a generational memory so that stake weight follows a coin for a while after each trade. The generational weight can be reduced by performing useful work. That useful work itself could be bought and sold, but disappears when spent maturing the traded coin.
I guess I'm trying to brainstorm a system that requires everyone to participate in useful work of unpredictable efficiency, where stability is added by punishing frequent exchanges, and holding the coin heals the wealth gap. Basically, if you're just acquiring money to 'have money' the system will deem you less important than someone acquiring money to 'use money', but forgives somewhat if you give back in computing power.
Just spitballing. I'm sure I'm missing a ton of details, but it was a fun exercise for me.