Imagine if you can produce 3D compute substrate as 1 liter modules that can be built as Lego's. With holes to run water-cooling pipes through. If you have, say

Imagine if you can produce 3D compute substrate as 1 liter modules that can be built as Lego's. With holes to run water-cooling pipes through. If you have, say, 100l of such substrate for less than $10,000, with a density similar today's tech, just in 3 dimensions, you can probably afford to run most of it at very low frequencies to conserve energy, with only non-parallelizable operations running at GHz-level frequencies. Such a machine could still probably provide as much compute as a small datacenter can today. Now I don't know if it will take 20 years or 200 to be able to do something like that, but I'm certain that we have a looong way to go before we reach the physical limit to how much compute we can stuff into a rack.