Indeed. The moment these LLM brains are given access to natural selection and evolution in the hardware space, it's game over.

We don't need to engineer plumbing robots - they will engineer themselves. We will see a silicon Cambrian Explosion. Maybe next year maybe in 500, but it's inevitable with the current economic incentives.

What if the creation of such robots destroys the economic incentive for doing so?

Bold of you to assume that “current economic inventives” will remain around for 500 years, especially given the American-style neo-liberal economy is only like 70 years old.