If heat is produced by conductors resistance then shorter paths would lead to less heat produced.

That's always an issue, but the industry seems to be moving away from 2D circuits.

Reducing trace length seems to be the way forward for faster/larger circuits. Signal propagation time on-die is becoming an issue.

Things like Huawei's Logic folding, or TSVs, and so on, attack the issue by reducing signal travel time.

This looks like another building block in that direction.

There's also some push at cooling chips from both sides.

I wonder if the proposed CPU/GPU laser cooling technique that was on here a few days ago would penetrate the Si layers?

https://news.ycombinator.com/item?id=48510375

What you loose in heat you gain in speed caused by proximity. Perhaps this will allow for lower voltage and thus less heat.