Is RAM even fast enough? I remember reading somewhere that the high speed cameras have special cache-like memory on or near the processor that is faster write than RAM. I can't find it now though so I'm taking it with a grain of salt.
Regular high-speed cameras that shoot a video are a whole other story, though.
https://www.phantomhighspeed.com/products/cameras/tmx/7510
The spec sheet lists up to 512GB of RAM depending on configuration. There's no way you're scaling cache-like SRAM up to those numbers.