According to: What happened at the Zcon0 mining workshop (and more...)
“Another hardware manufacturer also said that changing the parameters would be incompatible with their hardware. However, when asked if a firmware update could handle new parameters, they said yes. When further quizzed to clarify if this was because the hardware had sufficient memory for a parameter change, they said no, but that it might be possible to add more memory.”
And how long would adding more memory take? Almost no time at all.
Meanwhile, after they successfully add memory, how likely are they to sell this new hardware to the public if doing so would cause another parameter or algorithm change a few months later? It’s very unlikely, because they wouldn’t want their more efficient mining hardware invalidated. Innosilicon would just mine it in secret or sell it secretly to existing large farms, excluding home miners. Then you end up with a situation where some miners have a huge advantage over others, potentially threatening network security.
This doesn’t even account for the situation where you’re leaving the network insecure after a rushed parameter change. If Zcash just happens to be less profitable to mine at that time profit-driven GPU miners won’t be interested in mining zec.
I think you’re vastly underestimating hardware manufacturers. Keep in mind that Bitmain made more than Nvidia last year. They have access to anything Nvidia can put on a GPU, including more memory.