Thanks to TSMC's new stacked wafer manufacturing process, future CPUs and GPUs could double the performance just by integrating dies with two wafers. For now, only two wafers can be stacked one on top of the other, but in the future, dies could include multiple wafers and get a vertical design, instead of a horizontal one. The only problem is current dual-wafer designs have low yields for manufacturing processes under 16 nm, but TSMC is working to improve that.
https://www.notebookcheck.net/AMD-and-Nvidia-future-GPUs-could-integrate-TSMC-s-new-wafer-on-wafer-tech.301836.0.html