From my memory of the asic race it would take 6 months at least, probably closer to a year, but that's not important. What I'm considering is that it would be necessary to change PoW in the case of a hard fork simply to avoid the risk of attack from the existing sha256 mining hardware..

On the less popular chain, blocks would grind to a halt under the existing difficulty. If we assume 10 percent remain then you would expect 1 block every 100 minutes, at least until the next difficulty adjustment, which would be a very long time because difficulty is adjusted every 2016 blocks. If you reduce the difficulty artificially to allow blocks to be mined and transactions to happen in a timely fashion then It becomes trivial for any mining pool to quickly switch over and mine a bunch of your blocks and then dump the coins...


I think, in the situation where one would want to cling to a minority chain after a hard fork, an algorithm change is essential.

Also, there is no incentive to design or build asics to run the new algorithm unless it is insanely profitable, as was the case when the first bitcoin asics came on the scene.