Manufacturing ASICs from scratch requires a lot of capital, but it is fundamentally possible. There is no way to acquire a permanent, unassailable monopoly over ASIC hardware in general.

It is possible to acquire an unassailable monopoly over PoS tokens. You might be able to buy scraps from random traders, but will the >51% whale be willing to sell their core holdings when they can simply live off their staking yield?

>A permissioned blockchain is one in which the ability to add blocks is limited to a certain collection of entities

I agree. Ripple is an example of a chain which explicitly follows that model. PoS regresses to something like this because a 51% majority attacker can control consensus.

> There is no way to acquire a permanent, unassailable monopoly over ASIC hardware in general.

Is ASIC hardware made of silicon? In that case, an entity who owns the entire supply of silicon has a "permanent, unassailable monopoly over ASIC hardware in general".

I hope you're joking?

Silicon is the second most abundant element in the Earth's crust, after oxygen: and only because there are two oxygens in silicon dioxide.

If someone corners the market on silicon, Bitcoin dominance is the least of our problems.

OP's argument is that PoS is a problem because the supply of tokens is finite, and that PoW doesn't have the same problem because it relies on physical capital instead.

But physical capital is also finite.

What are the advantages of a permissioned blockchain over the same collection of entities without the blockchain? If you have a set of trusted entitites that sign and publish the data, why do they need the blockchain part?

One entity can sign and publish the data, but that doesn’t mean everyone agrees with it. If everyone agrees, they yes they could all sign the data as well. And if the ordering of the data is important, might as well put in a pointer to the previous data. And now we have a blockchain!

You're right, a set of trusted entities don't need a blockchain! It's a terrible datastructure which only makes sense in a very narrow circumstance.

Followed through to its ultimate conclusion, a set of trusted entities should simply run some kind of performant database.

I also generally understood permissionless to mean sybil attack resistant without closed membership which is the unique property of pow and pos systems.

The inability for anyone to modify the hard coded public keys makes it permissioned.