You can't get something for nothing forever.
I agree with this general observation for what is going on right now. It very accurately explains why Bitcoin is worth so much per coin and every single PoS coin is worth very little. But in the long game, I think the cost of maintaining the PoW system (because it requires so much work) will start to tax the system (especially when the subsidies expire). Where as with a different proof-of-x system in the long game, it will be cheaper to maintain the system, thus making the coins ultimately more valuable.
Both provide essentially the same utility, but one has hire taxes.
This of course would assume that all things being equal. When in fact they are not. Right now Bitcoin has a huge first mover advantage and a better marketing advantage. Those alone might make it very difficult to disrupt even if a different platform is technically superior.
By "tax" the system, I mean just that. The miners are charging taxes on transactions. Right now that tax is $0.04. There are about 100,000 transactions per day give or take. That is going to mean that about $4000 in fees are being paid to miners by people wanting to have transactions processed. Yet, the miners are getting paid $1,300,000 a day. So who is paying for the rest of those miners to run? They are regularly buying new hardware and electricity. Where does that money come from? It comes from the rest of the system getting taxed (existing bitcoin holders getting devalued).
So when I am talking about the system being taxed, I am talking about all the money that it takes to buy new hardware, maintain it, and power it with electricity. It is taking a ton of work to maintain the Bitcoin blockchain. That money that those miners are using to pay for electricity and hardware doesn't just magically appear. Maybe the miners are not cashing in the whole $1.3 million a day, but I am guessing we can safely assume they are cashing out more than a million a day. That is a million dollar tax (minus $4000) a day to keep the system a float. If they don't get their million dollars, the whole thing falls apart.
Now, to your question of "if" miners were able to mysteriously come up with hardware at a cost of near $0 and run it for a cost of near $0, then yes, there would be virtually no tax at all on the system and very small fees would cover the cost of the miners. In that case the Bitcoin blockchain could be managed and maintained for very cheap. I am guessing that would be a great thing not just for Bitcoin, but for the whole world.
But if you want to talk about a system where the maintainers of the blockchain are having very little expenses for electricity and very little expenses for hardware to run nodes, then we should talk about some of the current PoS systems, not a hypothetical Bitcoin blockchain of a possible future. For instance many platforms like NXT and NEM have shown that their nodes can be run off of a $50 Raspi B+. Those in turn can be outfitted to be solar powered (though at that point it is probably just cheaper to pay for the minimum amount of electricity).