Ray Kurzweil has long predicted 3D computing chips would become a paradigm. I'm not talking about GPUs, but actually vertically stacked layers of transistors. https://www.kurzweilai.net/radical-new-vertically-integrated...
A big problem is heat. But stacked designs produce less heat overall, just in a smaller area. That can actually make heat dissipation more centralized and more efficient (due to higher thermal gradient) so I think it's a solvable problem.
I do agree, the longer term will lead to stacking, I'm just not sure how far off that is in realistic terms, and if the complexities may outweigh the benefits in a lot of use cases.
The node shrinks are definitely slowing and have for a several years.