You can go up to 4 GPUs with very high-end motherboards in an ATX box and I guess, after that, you are in the "specialized hardware" territory anyways? There ar

You can go up to 4 GPUs with very high-end motherboards in an ATX box and I guess, after that, you are in the "specialized hardware" territory anyways? There are also graphics cards enclosures which work through Thunderbolt/USB 3.1 and I'd bet they have enough bandwidth to max out the cards. But I wonder how crazy you can get with the number of cards.