I don’t know which subreddit this belongs into and I am not so familiar with the hardware details, but what is stopping you from designing a custom PCB that connects an off-the-shelf high bandwidth arm cpu with several low capacity high bandwidth commercial (graphics) memory modules for eth mining? You could save money over a gpu that has extra chips and features you don’t really need.
Im probably wrong for some reason: Is it technically unfeasible or won’t it be better than a normal gpu? Maybe you need special hardware that can’t be bought? It seems to me that ethash mining only needs high memory bandwidth to at least 4.5 GB of ram and that the computing part isn’t that demanding.
from Ethereum https://www.reddit.com/r/ethereum/comments/mgeead/custom_ethereum_mining_board/