Bitcoin Cash miners may be fired if they do not stand up to defend BCH from any 51% attack with Amaury Séchet, lead dev of BCH’s main client, BitcoinABC, stating:
“Changing PoW is somewhat of a nuclear option so I’d be reluctant to use it. But it always has been considered the option of last resort in case a large portion of miner become hostile, so we should be ready.”
A change of Proof of Work (PoW) means all current asics would be unable to mine BCH, with CPUs and more likely GPUs able once again to produce sufficient PoW.
That would instantly neutralize any 51% attack as the amassed asics datacenters of the attacker would no longer be able to produce PoW for BCH.
“It’s better to be ready and not need it than to need it and not be ready,” Séchet publicly said.
The work may have already been done for them. Luke-Jr of Bitcoin Core coded a Keccak PoW algo during the blocksize debate in 2016.
As BTC and BCH generally share much of the codebase and the current PoW algorithm, the above could very easily be incorporated if necessary.
Its necessity is quite unlikely. Some 90,000 asics are headed towards the remote regions of China and Inner Mongolia to overpower any 51% attacker.
The threat of a PoW change itself should moreover be sufficient because the attacker would lose all of his mining gear and get nothing in return for the attack would instantly fail as soon as the PoW algo change is activated.
Which may be why we have never seen a 51% attack on a main coin. There have been threats of it, but they have not been followed through so far.
Whether that will change this Thursday remains to be seen, with Calvin Ayre and Craig Wright allegedly planning a spam blocks attack to fork off other miners.
That might work if they gain and maintain 51% of BCH’s hashrate, which seems unlikely, and even if they do, they’d be forked off with a PoW change.