This is great! But what if the US invests 1% of GDP in GPU datacenters and then those are not needed becaues someone created a much more efficient architecture?

More efficiency just means more consumption. Think when they add lanes to a highway, traffic gets better for a little bit but very soon the highway is just as congested as before.

Look up Jevons Paradox, when something becomes more efficient, consumption can goes up, often due to price elasticity.

Think of like this: Imagine car prices go from $200,000 to $$20,000 - you wouldn't sell 10x the amount of cars, you'd sell --- In fact I just looked up the numbers - worldwide only 100K or so cars are 200K & higher, whereas roughly 80 million cars are in that affordable category.

So a price drop of 90% allowed sales to go from 0.1M to 80M!! I think this means we need more engines, tires, roads, gas, spare parts.

Then they'll be able to use those datacenters much more efficiently.

They will still use capacity. Why would you believe anything different?