Miner concentration that occurs when PoW is so easily unrolled onto ASIC — which is to say when the PoW is not memory, storage, and memory<->storage bandwidth demanding, will always lead in the end to mining concentration with the most marked advantage landing in the hands of manufacturing concerns.
It is true of course that any process that can be done in commodity hardware can be done better, faster, in specialized ASIC. But with Bitcoin we have a single easily unrolled hash function buzzing a small piece of header data with only a very tiny nonce getting incremented between operations. Tiny, tiny, tiny amounts of memory per hash instance, nil requirements in terms of storage, and zero need for high bandwidth memory <-> storage.
More and more parallel hashing instances per chip, smaller processes, and economies of scale lead to centralization especially in the hands of the manufacturers.
That centralization leads to power, and as the entirety of human history proves, power has a corrupting influence.
We see this today in the reporting today regarding remote kill functionality in Bitmain miners.
We see it more generally in folks like Bitfury who do not offer consumer level mining equipment, and would rather sell monster shipping container sized rigs to monster sized customers. (If you have to ask how much it costs you can't afford it).
Now, forgive me, but I cannot resist dropping an "I told you so" to all of the brazen UASF BIP148 supporters. I've been urging caution and getting a lot of crap for it. But imagine how a UASF chain fork would have gone if the UASF chain were not only a shorter chain at the outset, but the Antminer hashpower on that chain got remotely bricked in the middle of the process to see which fork would survive.
At any rate, I'd say its time to put a plan in place to at least be READY to roll out a new PoW for Bitcoin within an 18 to 36 month time horizon.
Its very extreme to think about, but ask yourself: Could you have ever imagined anything like the matters that are prevalent in mining these days? Pools refusing to implement broadly supported and very well tested protocol upgrades. Covert, patented, optimizations. Remote kill code in a crushingly large segment of deployed mining hardware.
Hell, the mere fact that it is possible to get 5 human beings in a single room and, among them, have an overwhelming majority of hashpower spoken for is worrisome enough.
I've seen /u/luke-jr post about the potential need for such a change before. I would love to hear if /u/nullc or any of the other core devs have considered the circumstances where a PoW change would need to be considered. Perhaps if there were a crypto break of SHA256 for example.
Just my thoughts at present.