> Density is a very important factor in datacenter design.

That's true if you're putting the chips in your own data center, because density affects TCO.

But assuming that Google does not sell TPU hardware, this isn't an important metric to anyone other than Google. The question that is important is, what does the shape of the curve plotting "dollars spent" versus "time spent waiting for my model to train" look like?

The shape of that curve is affected by TCO, and TCO is certainly affected by density. But there's a lot more to it than that.