The big barrier remains heat and this 3D stacking (aka CFET) makes heat worse by increasing density. It's possible much of the density gains offered by CFETs will remain unutilized unless other approaches to solve the fundamental heat problem are found, possibly discovering new high-conductivity MDI materials.
https://semiengineering.com/the-race-to-replace-silicon/
https://www.plantengineering.com/semiconductor-material-that...