You could. Tighter cooling integration for denser ICs is an area of active research but is something that needs to be economical at scale to matter. If a rack f

You could. Tighter cooling integration for denser ICs is an area of active research but is something that needs to be economical at scale to matter. If a rack full of flat chips does more work per dollar than a complicated-to-manufacture 3d-stacked coolant-permeable IC, there's not a very strong argument for building them. Peltiers are inefficient as all hell and not likely to be part of such a tightly integrated solution.