That is a very well thought out and technical rebuttal to my pipe dream. Thanks for ruining christmas.
My (unskilled) thinking was that scrypt is ram heavy, ram is pretty cheap these days. Math, on the other hand, is not my strong suit. Thanks for the perspective and publically abusing limitless in that thread you linked to.

dram size is cheap, sram is expensive, and bandwidth is very expensive.
GPU can easily have more than 300GB/s bandwidth, but FPGA less than 30GB/s.
IF there exists a FPGA can reach a bandwidth >100GB/s, I think we can do it.