Here is a discussion that I don't pretend to understand on stack exchange of how memory "hardness" may block ASICs by not allowing their faster processing time to be effective:
https://crypto.stackexchange.com/questions/29890/memory-hard-proof-of-work-are-they-asic-resistant/39784
This would seem to indicate that changing the algorithm is not the only factor. To my limited understanding, it might mean the chip architecture itself might have to be changed. Bitmain is not going to send you replacement chips when the X3 doesn't work for Monero.
Off topic, but I was very surprised that the Sia developers did not try to block the A3.
I can't help but see Bitmain as an obstacle to the viability of crypto-currencies.
Some of the developers of Monero are advocating making the currency completely not able to be mined. Interesting idea. You can mine gold, you can mine diamonds and other traditional tokens of value, but you can't mine dollars or any other fiat currency.