They have to be build though, which is expensive. If the hashing algorithm is parameterized by the block number in some smart way it will be harder to deploy th

They have to be build though, which is expensive. If the hashing algorithm is parameterized by the block number in some smart way it will be harder to deploy them. For example, one could use 10 different algorithms and choose a new one every block. The ASIC will only work 10% of the time but this can be implemented on the GPU. I agree that FPGA resistance is much harder to achieve.