One theory is that Elon Musk ends up being able to build AI datacenters faster and more cost effectively than anyone else, which seems plausible given the success of Tesla Gigafactories.
There's some stuff you can do with Combined Cooling & Power or other cogeneration schemes, and potential for cost-cutting: removing fire protection, doing without redundant power, reducing security, that sort of thing. But that's all fairly marginal in the grand scheme of things.
The more experimental stuff like running with extreme temperature gradients, extensive liquid cooling, or maybe using CO2 or He instead of air is certainly worth trying out, but unlikely to make much of a difference either.
SpaceX are claiming that they're making a big profit on their deals with Anthropic and OpenAI but that seems to assume that the cost of the compute is zero. I'm not a forensic accountant, so maybe it's okay to have written the value of that down already, but it's not a trick they'll be able to pull off more than once.
Really, the best thing you can say about them is that they've got a big pile of money so can finance capital expenditure cheaply. That gives them an edge of a few percentage points over the likes of Equinix (worth $14.2bn), but not much more than that.
It could be close-to-free labor, subsidies, or a myriad other things... but it's something.
Some links:
https://x.com/maxiaoalex/status/2062910018840854722
But mostly this one: